Krag bolt interchangeability

[Parashooter]

. . . (I am not clear in my mind if these are Chamber or Case dimensions)?

As indicated in the drawing, that's chamber. Here's the cartridge drawing (with .303 for comparison) -

303v3040saami.gif (63.56 KiB) Viewed 1307 times

[butlersrangers]

Parashooter - Thank you very much for the clarification and additional data!

[FredC]

Parashooter,
I am really confused now as I did the simple math of subtracting .063 (Remington max as tested with a fixture) rim thickness from the 1.7251 shoulder length on the saami drawing and I get 1.6621 which is way longer than lengths in appendix 9 http://www.kragcollectorsassociation.co ... 962#p38962
for the post 1899 chamber a fuzz too long for the pre 1899 drawing. SAAMI does not give a tolerance for this length and it is difficult to measure with the radius on the corner of new brass. Do you think the appendix 9 drawing is suspect or that all Krags were later reamed deeper? Something is not adding up, my math or one of these drawings is wrong?
If I am making a stupid math error lay it on me as this is going to keep me up at night if I can not figure it out.

[Parashooter]

Your math seems right, but it's based on what appears to be a pretty rough sketch compared to a reasonably precise 21st century engineering drawing - neither of which may reflect abnormal outliers in real steel and brass. Stop before you make yourself crazy!

FWIW, CIP's "L1" dimension, 43.82mm, is virtually identical to SAAMI 43.818mm -

CIP3040.gif (43.37 KiB) Viewed 1289 times

[butlersrangers]

To help Fred sleep, here is another drawing to count and ponder. It is from a 1917 manual for the Krag, that was likely reprinted from an 1898 or early 1900's "Rules of Management " booklet.

The dimensions are for a cartridge with the old 3-groove projectile.

The dimensions .18" plus 1.64" give 1.82" from the cartridge base to the start of the case-neck. This closely agrees with the SAAMI standard of 1.8289".

The total case length of 2.314" in the old drawing, matches the SAAMI dimension. Also matching, are the rim diameter tolerances, .545" to a minimum of .535".

[butlersrangers]

FredC - I have not been able to find more information on the chamber diagrams that Frank Mallory used in the "KRS" or locate anything similar.

I did find an 1898 Frankford Arsenal diagram for the .30-40 cartridge.
Unfortunately, its numbers are a bit different and add up to 1.854", from the back of the rim to the junction of the neck & shoulder, which exceeds SAAMI standards.
However, everything adds up to 2.314" which is the correct maximum case length.

Crazy! Oh well, most Krags and ammo are amazingly trouble free!

[FredC]

Thanks Parashooter and Butlersrangers maybe I will get some sleep tonight. Those early drawings have to be defective. No other explanation, if there was a correction made later some Krags would have missed the corrective reaming and we would be having night mares with incompatibility today. Grafs's cases seem to be an outlier that are catching only on a thin ring of material in the middle of the angle. In Grafs's defense these SAAMI drawings are made to theoretical dimensions on the shoulder in practice the cases have a radius on the corner which makes measuring the case difficult as there is no sharp point to measure from. I tried the Grafs cases in my 35/40 which was cut with a SAAMI specified reamer, and a couple of the cases barely had an interference fit with a very faint line showing on the angle most chambered with no issues.

I am going to say that arsenal made barrels where reamer life was pushed and reamers resharpened till they could not be sharpened again and that is why we will see some Krags that do not like Grafs brass.

One more question for Parashooter, when you are setting up a full length sizer die your press do you compensate for the fact the press will stretch by making the adjustment a little tight when adjusting the die? Seems like a properly adjusted full length dies should fix the problem without modifying the shell holder. Seems like a properly made die and shell holder should always resize to a smidgen smaller than the SAAMI specs. We discussed forces and frame stretch in this thread at Practical Machinist https://www.practicalmachinist.com/vb/g ... se-384868/

Zac, let us know how the resizing works.

[Parashooter]

Guys, please look again at the 1898 blueprint and note that the shoulder lines are drawn not at an angular intersection but at the origins of the double radius (ogee) which is how the shoulder is drawn there. You can't compare the resulting length dimensions to lengths defined by angles as on the SAAMI and CIP drawings.

KragRadius2.gif (326.18 KiB) Viewed 1249 times

As for F.L. sizing die adjustment, my habit (for manually-operated rifles) is to adjust so cases are sized only far enough to chamber with a slight but palpable resistance in the last few degrees of (stripped) bolt closing. Here's some detail from Sierra on how -

Setting dies for your rifle: Minimal resizing.

Begin by removing the decapping assembly and turning your full length die into the press until it contacts the shellholder at the rams highest point of travel. Back the die out one and a half to two full revolutions. Find a case that will not chamber easily in your rifle. Resize it, and try it in your rifle. It probably won't chamber easily, so adjust the die down by another eighth turn. Resize it again, and try to chamber it in your rifle again. Continue this until the bolt will close with some pressure. Continue to adjust the die downward by a sixteenth of a turn at a time, until the bolt will close with a slight "feel."

This procedure naturally compensates for any press/die flex encountered.

[Zac952]

I have resized them with an RCBS full length resizing die set to contact the shell holder plus about a quarter turn or so, I have an old RCBS press and I can feel the cam over is fairly tight, but it doesn't even bump the shoulder back at all, it is an RCBS shell holder also matched to the die set. Not sure if this die is off or not but it was new ordered from rcbs around my first post, April or May if I recall.

[FredC]

When it cams over (locked with the handle all the way down) is the shell holder touching the die? If it is you can go no further without removing material off the shell holder. Some of the resistance at this point is resizing the body taper as well as the neck friction. Using Parashooter's idea with the 308 die would clear the body so beside the neck friction you would have only the pressure from actually moving the shoulder back. The angle is within about a degree and 1/2 off which is negligible.