On another KCA thread recently, a new member asked about the meaning of the odd markings on his model 1898 Krag bolt.

The best guess, I could offer, was that maybe they identified steel lot, production period, or a bolt passing inspection steps or proof testing.

(1903 Springfield authority, John Beard, on another forum, has provided his research in the form of "Steel Lot Code Charts". These just pertain to 1903 Bolts, and help identify year ranges and manufacturer. Some of the earlier codes are simple & odd letter and number combinations. Possibly, this could be the purpose of the markings we see on our Krag Bolts)?

Some KCA members speculated that the markings might relate to certain bolt dimensions to assist proper head-space and function.

FWIW - I examined six model 1898 bolts and one model 1896 bolt, today.
I noted their markings. Some of the  bolts, but not all, had a 'Rockwell like' punch mark, on the back of the bolt-handle. None of the bolts had identical markings.
(I could detect no regular pattern to the marking system).

I measured with a vernier-caliper: 1. The distance from the front of the bolt-flange to the rear of the locking-lug. & 2. The distance from the front of the bolt-flange to the rear of the guide-rib.
(These seemed easy and relevant comparison points to me).

Frankly, I was surprised by the closeness of dimensions from bolt to bolt.

Here is a tabulation of my observations.

---

Butlersrangers you are on to something there. I have thought of a way to measure actual headspace variation produced by the bolt. The attached photo shows a simulation of how I would do it. Bolt lug to the cartridge recess is the actual dimension to measure.
My V-block in the photo is close to a correct way. To make it better would involve honing a radius on one of the surfaces that would be larger than any on the lug. When the Krags were built it was already known that a radius in the corner would resist cracks from fatigue and also make the cutters last longer. That radius is not very big on Krags but it is there and not to be gauged from, you want to gauge from the flat part of the lug.
Just went back and looked at your photos but did not see the one I saw recently with a star stamped on it. I got a feeling that was one inspected all over and not just critical areas, kind of like a star gauged barrel. I think star gauged barrels were done when fresh tooling was installed and extensive gauging was done. Personal opinion is a star gauged barrel is not necessarily the most accurate. Maybe 10 or 20 barrels later the tooling settles down and actually does a better job.

Back to your on to something there, IF there were some variation in headspace that was addressed during final assembly, I really doubt it was by just going through a bucket of random bolts. IF there was any final fitting is was with known bolts that were plus and minus from a mean dimension and designated by a now unknown mark.

I started a discussion on Krags on another forum, particularly about head space and timing or clocking of the barrel.   (You need to Login
So far a few interesting comments and some guesses. I doubt the Springfield A guys were measuring to 50 millionths of an inch.

---

Fred - Neat precision measuring fixture!

Attached is a photo of the markings on the rear of model 1898 bolt #5 (star marked) and 1898 bolt #6, (as recorded in my chart).

It would be interesting to know the variation shown, on a large sample Krag bolts, for the measurement from the front of the bolt flange to the actual 'recessed' bolt face.

---

FWIW - I got to thinking (always dangerous) and started measuring the depth of the bolt-face recess on four model 1898 Bolts.
(The distance from the front edge of the bolt-flange to the bolt face, near the firing-pin hole).

Bolt condition varied from 'visibly worn' to 'new old stock' and I took five measurements on each bolt-face. I rotated each bolt so as to measure in different spots, using the 'depth gauge' provision of my vernier-caliper.

I found, I was getting .005" variation between my minimum and maximum depth measure on each bolt. The NOS bolt only showed .003" variation.

The maximum bolt-face recess I measured was .066".
The minimum bolt-face recess I measured was .058".
(This difference is less than the thickness of two sheets of typing paper).

I averaged the five readings, I obtained, with each bolt.

For all four bolts, the average of five depth measurements came to .0608" (basically, 61/1000 of an inch depth, from front of bolt- flange to recessed bolt-face).

I found it kind of amazing each bolt gave the exact same average. (.0608").

I know where I had seen the star now it was on your hand written list. Probably means the same thing as on a barrel, all dimensions checked and near the mean. Maybe like a first article inspection after tools are changed or the whole set up is refreshed.

On these drop indicators the gauge tolerance should be 1/2 the smallest division. The smallest division on this one is .0005 inches but I have never verified that it is really that accurate. With dial calipers the same rule applies about 1/2 a division, with digital you can not split the last division so I do not know what the rule is there. In a production shop we never trusted calipers for anything closer than a Plus or minus .005 tolerance. That was a long time ago before good digital calipers became available.  I still follow the old rule in my shop as I can find a better way for production measuring with indicators or specialized mikes. Mainly use calipers for quick reference.

On the depth of the recess I would not have held that as close if I was making them. Close tolerance is always costly only do it when necessary and that is the lug to the recess. Measuring with calipers is a little iffy for precision. I would be more comfortable with a depth mike, but one place I worked at called depth mikes Volkswagon bumper jacks and despised them. We used them in production shops and were comfortable holding .001 with them.

What does NOS stand for exactly, I am taking that it means no visible wear.

I too would like to see a bunch of new ones measured. I am trying to think of a safe way to check about 10 from Dave at Grandpas or making a quick and dirty gauge that would be repeatable and could be easily shipped to you and maybe Dave to check a bunch of bolts.

"NOS" means New Old Stock - Old parts that were never used and that are in new condition.

BTW - My favorite vernier-caliper was my Dad's. It has no Dial. You use the increments that lineup exactly.

I was never a Machinist. Just, the son of a good one and I took an interest in his work.

I made a mistake and thought about that gauge too long. Not possible to make a quick and dirty gauge now. Thinking is dangerous!
Found a length of seasoned gray iron, milled it square and milled the ends also. Surface ground it top and bottom and milled the 5/8 channel. I was going to mill a groove to clear the bolt guide but that would have required a stand under the gauge to clear the hanging bolt handle. Decided to mill a stop to support the bolt handle instead. This keeps the bolt from camming out of the channel from the weight of the handle.
Need to make an indicator holder and a gauge for zeroing the indicator and it will be finished. Regular work keeps getting in the way, but another week or two and it should be finished.
BR, can you line up some more bolts to check and note the markings?

---

Almost got caught up in the shop and did some more work to this gauge. Special length screws will be here in a couple of days so the parts are just propped up to look like it is assembled. Need to make the indicator end and a zero setting gauge and it will be complete.
Way past quick and dirty, I thought about it too long and made drawings of the various parts. If I ever think about doing this again will someone kick me real hard, please.

---

Assembled the gauge and got 2 measurements from my 2 Krags. First photo is setting the zero on the gauge.
Second is my sporter bolt (Assembled) measures .450 plus the indicated .0175 or .4675 total. (small dial reads .450) Ser #410XXX
Third  is my fathers relatively unused bolt (Stripped) it reads .450 plus .0278 or .4778 total. ser #397810
The markings are similar on these 2 bolts.

Stripped bolt on the back has sideways V underneath S12 and a punch mark, bottom flat has a 0 (zero).

Assembled bolt back S12 underneath 0 and a punch mark.
Bottom flat F.

The wear on the assembled bolt left a small unworn patch that caught on the gauge, the pen in the photo was lifting it so that patch was not touching. Indicating the wear to be about .005. These 2 bolts with similar marking and serial numbers were probably .005 different when new. That is almost the whole head space tolerance.

The rifle with the assembled bolt was probably last used by my father in 1940 as he was mobilized in 41 and hunted with his 1917 Enfield afterwards so it has very little wear.
I plan on milling a small pocket on the gauge to clear the unworn portion of a bolt so it will give a closer to effective measurement.

2 bolts is not enough to mean anything yet, but indicates some caution be used when swapping bolts, especially if wear is evident.

---

Well I finally got the gauge finished and built a "package" to protect it during shipping.
Since Butlersrangers originated this thread with the idea that the markings on the bolt could possibly indicate a plus or minus dimension from a "mean" that would help with final assembly, I will send him the gauge first. With the checking of many bolts we might be able to discern which if any of these marks may indicate plus or minus dimensions. BR has indicated the marks might indicate lots of steel, other may indicate the shift or which line the bolt came from.
With the .009 inch difference I have seen measuring 2 bolts with an "s12" stamp on the back I would not recommend to anyone that bolt swapping is OK. These 2 bolts may have measured the same when they left the armory but the one with the more extreme wear was shorter.
So I will pack it tomorrow for sending to BR. I will also make a printable chart for recording the info. BR's chart on the OP looks good to me, right now I would add a line for shift while closing the bolt, I saw .004 to .005 inches on mine. This shift may be universal on all of them, it will be good to know this. I would like a copy back from each member that uses this gauge to check his bolts. I recommend you do one a time to prevent mixing them up.
If you have a Krag that closes on the field gauge and is loose on that gauge, the info we compile here may make it easier to get the right bolt to get the headspace back to a better range.
Two videos on using the gauge. The first is longer and shows more details on packing, the second is from a better angle and shows more details on actual measuring.

  (You need to Login   #1
  (You need to Login  #2

Any suggestions on details for the chart or the videos will be taken into consideration.
If you want to get in on this exercise send me a PM, with your email address and how many Krags you have to check, especially if you have any new old stock on hand.

Thanks for taking the time to make such an informative video and developing the tools and demonstrating their use.
I think the video (s) are very well done.

Maybe the marks represent the worker who went back and finished or gauged the cock on opening ramp, and did final polishing/fitting of the bolt lug or drilled the gas escape hole checked bolt face etc.
I'm starting to think the marks didn't have anything to do with headspace. The letters numbers and marks might just reflect payroll or tool room or equipment logs. Maybe even for machine ID in case a tool became out of spec before the rifles made it to another station during manufacture so it could be identified for maintenance or adjustment.
Just a guess on my behalf, they seem to be too randomly done.

I bought 2 new old stock bolts from Grand Pa's and both had an S17 stamp on the end. Both measured .477.
With the clearance filed onto the gauge for worn bolts my Dad's bolt with very little wear now measures .475 consistently.
The observed change while closing in the used bolts is also seen on the new bolts so it is designed into the bolt to cam in on closing. Will post more observations on these new bolts as seeing them new reveals many of the steps used in making them.

One of the first surprises examining the new bolts is the manner of finishing on the bolt body. The round out side diameter surfaces are all ground. Next to the bolt guide and locking lug a wheel with a radius dressed into it was used and transversed length wise to get the round diameter next to the guide and lug, other round surfaces a conventional cylindrical grinding pattern is observed. On the mostly unused bolt I can discern the same marks now that I know what I am looking for.
Next surprise the locking lug's working surface is NOT ground. It shows machine marks as well as the case hardened surface. This will give a way of guessing at wear of the bolt.
The first attached photo shows a bolt that has not been used in 80 years as well as one of the new bolts. The lightly used lug shows a shiny spot (circled) covering about 20 to 25% of the surface. So most of the lug has never touched the corresponding surface of the receiver. This bolt has an s12 mark on the rear. This is too few samples to be sure but a wild guess would say the s## may indicate a .0004" or .01mm increment.
Surprise #3 the new bolts have a number of dings. A ding besides having a indentation will have raised metal on the sides which could roughen the perceived feel and wear the receiver. I circled them with a marker and found 7 on one and 13 on the other. Made me wonder if they came from storage or SA, then I looked over my 2 bolts and they had dings also, most have had at least a portion of the raised material worn off. So I am going to say the dings came from the arsenal and not from Grandpa's. The packaging and box from Grandpa's were completely adequate. I will touch all of them up with a Cratex wheel in a Dremel tool. The grit from this kind of operation is one that will keep on giving so clean up afterwards is most important. On the photos with the dings circled the new ones are on the left and the most worn one on the right. The used bolts have 10 and 3 dings respectively.

---

"Dings" on new Krag Bolts seem understandable to me, if we look at how they were handled, stored and shipped.

Joe DeChristopher's grandson describes packages of five new bolts: ... "part of just opened wooden crate, they haven't seen the light of day in over 100 years" ...

Springfield Armory (Hill Shops - Hardening Room) photos may show handling of 1903 Bolts, but, process for Krag Bolts was similar.

---

After my examination I came to the same conclusion. Since my 2 bolts in my Krags had the same dings.
Dave at Grandpa's did a good job of packaging and is providing Krag lovers with a way to make them last longer at a very reasonable price.

For those that have a Krag with similar dings massaging them carefully a fine Arkansas hone or careful use of a rotary tool with a Cratex rubber abrasive could make a Krag even smoother. This applies to a NOS or original bolt.
My sporter was head spaced to the original worn bolt so these new bolts will even fit. My dad's original rifle's bolt in automotive terms is not even broken in so I do not even need these bolts, I just wanted to see them in person and add to knowledge her on this site with measurements and a description of what I found.

My reference to grinding marks is about how these bolts were finished, please do not think of someone holding a bolt up to a bench grinder, think more on the lines of a machine like a cylindrical tool grinder. Till fairly recently grinding was the best way if precision finishing hard surfaces. The grinding done on these Krag bolts is very well done and I am not sure how they pulled it off 100+ years ago.
If you can see those marks on a bolt in use that would be an indication that at least the bolt is fairly new, if it is an original bolt the gun has very little use.

Also I am not bad mouthing the work done at SA, making almost a half million bolts this complex is a real achievement, just explaining what I see. The attached photo does show the grinding marks in 2 directions on both new bolts. take a look at yours and see if you can find them now since we know what they look like.

---

I have two Krag bolts that would fall under the title "New Old-Stock".

One is a model 1896 and the other is a model 1898. They do not appear to have been used on a rifle and, when I got them, there was lots of old cosmoline, that had to be removed from the exterior and interior.

To the quick glance, these bolts appear quite new, similar, and factory bright.

Upon close scrutiny, there are slight nicks, bumps, abrasions, and minor rust spots.

These bolts operate very smoothly in any Krag action, I have tried them in, and they tighten up head-space or free travel.

God only knows how many miles these bolts have traveled, greased and wrapped in paper bundles, that were stored in wooden crates.

Kind of like when New Coins are shipped from the Mint in bags. They come out bright, but, with storage marks.

IMHO - Every young man should have a NOS Krag Bolt in his Man Cave. 

---

I massaged one of these NOS bolts with a Cratex wheel to take of the high spots near the dings on and found another surprise, the inside of the bolt is flex honed or sanded. The smoothness here will  reduce wear and fouling on the firing pin spring. Who would know till you do a thorough cleaning and check with a bore scope.  Not sure how to take a photo through the bore scope otherwise I would do it here.

Well Butlersrangers has finished his bolt checking, in the interest of advancing Krag knowledge here, who else wants to check there bolts? If you have been a regular here for a number of years and have more than a few Krags send me a PM and we will see where the bolt checking fixture goes next.
I have to review Chuck's data but at first glance it appears that all the stamps on the bolts are going to be random as far as bolt size and head space is concerned. Further checking will be helpful and members that do check this will have a better understanding of their own Krags.

At FredC's request, I am posting a chart (recording the basics) on the twelve U.S. Krag Bolts, that I measured using his fixture.
(Fred's device precisely measures distance from recessed bolt-face to rear of locking-lug).

Eleven of my Bolts are model 1898 bolts. One is a "New Old Stock" late-style model 1896 Bolt (from Grandpa's Gun Parts).

Two of the 1898 bolts came to me in model 1896 Krag rifles that were refurbished in the early 1900's. Both bolts closed on my 'Field Gauge'.
  (I switched these two Bolts between the model 1896 barreled-actions. One Bolt 'worked' and no longer closed on the Gauge. The other action required a 'New Old Stock' model 1896 Bolt).

Six model 1898 Bolts are in the Krag rifle or carbine they arrived in. The bolts do not close on my .073" Field Gauge. (Fired Cartridge cases will interchange in the chambers of these Krags).

Four Bolt/Receiver combinations are known to be replacements. They also pass the Field Gauge test. (Oddly, the two bolts with the worst dimensions still pass in the receivers, I have put them in.

Two Bolts, (one NOS and the other showing some wear), are in my spare parts box.

Here are my results. I do not see a pattern to the markings.

---

Anyone with a batch of Krag Bolts, willing to precisely measure (bolt-face to rear of lug) and record measurements and markings, should contact FredC.

---

So, I'm next on the list to add to the data for Krag bolt measurements using Fred's wonderful Krag bolt gauge. Fred put a lot of time in making this accurate gauge set up for us to learn more about the detailed hieroglyphics on many Krag bolt handles and whether or not there seems to be correlation to the measured front lug of the bolt body.

I have a lot of Krag bolts to measure, so, I'll probably take a while but research is never quick or easy. So far, from Fred's and Chuck's (Butler's) measurements, there does not seem to be any obvious correlation.

After I'm done, hopefully more KCA members will undertake this exercise. This measuring and detailed examination of every one of my Krag bolts is really teaching me a lot about the Krags and I am thankful that I have been given this opportunity to do this. I have definitely been learning things about my Krags that I didn't know before. That's why we do these things, I guess.

I recheck zero every 5 bolts. I have been wrapping a rubber band around each bolt or Krag after measuring the bolt so I don't lose track of which ones I have done. I also am cleaning the bolts well enough so as not to affect precise measurements.

Thanks Fred and Chuck for the gauge, procedure and layouts that you have made in starting this project. I'll eventually finish this up and report back.

It doesn't matter how many bolts you might have to measure. You'll learn a lot by doing this and add to the database.

---

Hey Whig,
I have 2 Krags and only had 2 bolts for a long time and I managed to mix them up. I figured them out and got them correctly matched before I did the sporter build.  You are certainly braver than I am to pull that many at once, either that are you are superbly organized. The markings are probably unique for each bolt, I suppose if each one was ID before removing them I could keep that many straight.
Be careful.

Thanks, Fred. I have been trying to be meticulously organized with this exercise. Thanks for the opportunity to learn a lot more about my Krags and work at this additional organization. I didn't know that I had as many M1892 bolts as I do. I also found a number of M1896 bolts in M1898 Krags and vice versa that has allowed me to switch things around to make some of them more correct. I don't plan on shooting some of these so I don't think I'll be altering head space to any dangerous degree since we already know Krag bolts are mostly interchangeable.

There are a few small differences with Krag bolts that I have now learned to easily see after doing these measurements. I used Poyer's book mostly to examine all of these tiny detail changes of the Krag bolt over time. I have finished the measurements with my time off with Thanksgiving. Great little project for this week. I'll be copying the measurements pages and get them to you and Chuck for review. I haven't spent much time reviewing the results myself yet. I'll wait a few days and give the info some fresh eyes.

FredC wrote on Sep 20^th, 2019 at 4:38pm:

Next surprise the locking lug's working surface is NOT ground. It shows machine marks as well as the case hardened surface. This will give a way of guessing at wear of the bolt. The first attached photo shows a bolt that has not been used in 80 years as well as one of the new bolts. The lightly used lug shows a shiny spot (circled) covering about 20 to 25% of the surface. So most of the lug has never touched the corresponding surface of the receiver.

I had too much trivia in post #13, so I thought it may be beneficial to mention estimating wear again.

The most meaningful way I can think of to estimate wear on the locking lug will be to estimate a percentage of wear to original surface  area on the inside of the lug. So on the bolt on the right the shiny area(worn is about 20% of the original surface, so lets call that one 20% wear. If the whole surface is shiny we would call it 100%. If it is 100% it could have all the surface worn just a .001 inch (relatively new) or it could be worn and lapped .010 inches like my sporter, but the percentage and measurement together will give the best guess as to its current status.

---

Whig has emailed me that he has finished with the measuring on his Krags. Anyone else that would like to do this please send me a PM. It would save on shipping if Whig were to send it directly to next KCA member.

Whig kindly sent me a copy of his work sheets, today, recording measurements and markings he encountered on 58 Krag Bolts!!!

I compared his 'data' with my notes on 12 Krag Bolts that I measured and noted markings.

My impressions:

Whig and I have measured 70 bolts: 8 model 1892, 9 model 1896, and 53 model 1898/99.

The dimension measured was from the recessed "bolt-face" to the rear surface of the locking-lug.

1. On the sample bolts, this dimension ranged from .4600 inches to .4791 inches. (A difference of .019").

2. The average of the 70 measurements was .4736 inches.
(If I threw out the highest and lowest measurements, the average of 68 bolts was .4737 inches. The average for my 12 bolts was .4739 inches). Realistically, No Difference Regarding Averages.

3. 35 of the bolts measured below .4744" and 35 measured above .4741".

There was an amazing array of Letters, Numbers, Symbols and 'punch' marks on the 70 Bolt-Handles.
There were only a couple of pairs of bolts with markings that matched. These 'paired' bolts had different dimensions.

The bolt-face to rear of locking-lug dimensions did not seem to bear a relationship to the markings.

FWIW - It is my opinion the Krag Bolt Markings signaled 'steel lots', production batches, or some inspection process. They do not appear to identify different bolt sizes.

Still waiting to see my copy.
Some of the marks may indicate what line or shift was involved. As production of the bolts ramped up they had to be made on different lines. When a problem arose being able to ID which line was causing the problem would be important. Some marks are probably from different inspections and or inspectors.
Bolts are way more complicated than they look the locking lug, guide rib, and bolt handle are all indexed to so many degrees, besides all the linear measurements. Cam surfaces for cocking and on and on.

BR, I thought I was seeing a pattern in the SXX numbers with yours and my reports. If the SXX mark does mean anything it would be a late development to simplify rebuilds. Whig said earlier bolts had few if any marks.

'FredC' - If it is OK with 'Whig', I will photograph his data and forward it to you.

FWIW - The difference between the largest (.4791") and smallest (.4600") Bolt measurement was .019", or about the thickness of 4 sheets of typing paper.

If you throw out the extremes, (4 low and 3 high measurements), the measurements all fall between .4694" and .4780" or .0086", less than 9 thousandths of an inch variation, about the thickness of two sheets of typing paper.

The 45 bolts in the middle of the pack vary less than .005", (between the shortest and longest), the thickness of one sheet of typing paper!

Fred, Your copy should be there today or tomorrow. You just live farther away than Chuck does. I'm in Ohio. I have no problem with my info being e-mailed back and forth. Might be better not to put it all on the KCA directly. Good for any research use privately.

I'll wait a while longer before sending the gauge anywhere in case anyone else chimes in for measuring.

Dick, do you have any interest in getting this gauge to measure your bolts?

Thanks all,

Larry

For right now I will concur with Butlersrangers on used bolts the marks we were looking to as a guide do not mean much. On my known lightly used bolt and BR's and my new old stock bolts I thought I saw a pattern emerging. I hope to check more NOS bolts in the future to see if that pattern was real, which could be a help to members working with an excessive headspace.