Krag 30/40 and accuracy vs. chamber/throat

Ammunition, reloading, shooting, etc
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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

FWIW - It is likely that the bolts on many 'well used' U.S. Krags will close on a "No-Go" gauge.

The .30-40 "Field" gauge, (with a .073 to .074" rim thickness), seems to be a very workable standard for most Krag shooters.

Extending brass life, by minimizing 'case stretch' in the head area, is a great benefit to keeping clearance between the barrel-breech and bolt-face (headspace) in the neighborhood of .067 to .070 inches.
A NOS bolt is a practical solution to reducing the clearance between bolt-face and barrel breech.

Neck-sizing brass, when reloading, allows brass to remain 'fire formed' to the chamber.
'Parashooter' has provided the suggestion of using rings of mono filament fishing line, in front of the case-rim, to eliminate 'free travel' and hold a chambered cartridge against the bolt face, during initial case firing. (This procedure further improves case-to-chamber 'fit').
These interventions can all be used to minimize headspace issues in the U.S. Krag.

I don't really accept the opinion of how "excessive headspace" has lengthened the 'leade' or caused 'throat erosion' in an original Krag barrel.
It seems more likely to me that barrel issues in the barrel leade/throat area are likely the result of how the Krag barrel was actually chambered & machined and from the composition of early propellants and corrosive priming.

IMHO - Short case life and case-separations would be a more likely outcome from excessive headspace in the .30-40 Krag.

















g0
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Last edited by butlersrangers on Tue Sep 13, 2022 2:09 pm, edited 3 times in total.

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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

FWIW - The 1907 U.S. Palma Match Team had great success in Canada, (at 800, 900, and 1,000 yards), using UMC Ammunition loaded with a 203 grain "Hudson - Thomas" pointed bullet.

I have not been able to find out the Over All Cartridge Length, but I think the rounds could fit through the Krag magazine.
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FredC
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by FredC »

Let's make it a third on the not seeing headspace leading to throat erosion. If there is a connection the effect will be miniscule.
Not sure if it has been mentioned but reducing the headspace to closer to the minimum by the means described so far will make ignition more consistent because the case motion has been reduced.
My 35/40 had really excessive headspace, I think in the past someone lapped the lugs to make the guide rib into a working lug instead of just a safety provision. A new bolt would not have been enough. Machining the step on the face fixed it. The rotation that the step caused was no issue as there is no front sight and the extractor notch was milled in last after the correct location was found.

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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

Caution is always needed with gauges to make sure they are properly positioned!

In a past KCA discussion, it was realized that some brands of headspace gauges may give invalid readings. Excessive rim diameter can create a situation where the gauge fails to fit within the bolt flange. (See Attached Photos)

For proper measure, it is essential that the headspace gauge be in actual contact with the Krag bolt-face and not hangup on the 'flange'.

Caution is needed even with a properly working gauge, to make sure it is centered in the chamber, as the bolt is moved forward.

I recently noticed, (even with a correctly dimensioned gauge), it was possible for the flange of a 'worn bolt' to pinch the rim of my 'field' gauge and give an erroneous reading.

The bolt in question was well used but appeared initially to be a 'good' match with a barreled/receiver.

Everything was positioned horizontally.
As I slid the bolt forward, it stopped against the 'Field' gauge, allowing only a little rotation of the bolt.
However, when 'jiggled' a bit, the gauge centered in the chamber and bolt-flange. The (stripped) bolt suddenly rotated 'closed', fully into 'battery', through gravity alone!
The bolt was No Good in this model 1898 barreled/action. Headspace was excessive, but I was initially fooled.

A spare NOS Bolt corrected the situation and headspaced normally.
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reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

I see what you are saying so let me put it this way.... throat erosion is normal as is erosion of the barrel in the first 4 or so inches due to the intense combustion gasses. Exposing more of the throat leade, by way of excessive headspace, will increase that erosion footprint.

I will guarantee I have some normal erosion due to the length of the rounds I am loading after measuring the chamber area. I believe the erosion footprint is larger due to the excessive headspace that has been taken care of by the NOS bolt. The single lug on the older bolt is visibly worn.

I am not saying the excessive head space 'caused' the erosion, that happens normally... I am saying it extended the erosion area by exposing more of the throat to the above.

If you buy into normal wear as described above then it is simply a secondary effect.

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Parashooter
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by Parashooter »

reiver wrote: Tue Sep 13, 2022 10:16 pm. . . Exposing more of the throat leade, by way of excessive headspace, will increase that erosion footprint. . .
You might wish to consider the position of the case mouth during the normal firing sequence.

Image
1. The firing pin shoves the case forward, rim against the breech.
2. The primer detonates. If it's not heavily crimped in place, it backs out, shoving the bolt and barrel as far apart as it can.
3. The thin, forward part of the case expands to fill and grip the chamber while the bullet moves out of the case and down the barrel.
4. The solid case head can't expand and grip the chamber, so it moves rearward, re-seating the primer, stretching the case walls just forward of the head, and stopping when it hits the bolt face.
5. If (and only if) the amount of head movement exceeds the elastic limits of the case, the cartridge separates into two pieces.
HeadspaceNaramore.gif
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reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

In my case, the casings are shorter after use than before if virgin casings, as I only neck size they stay about that but will stretch a tad during re use.... due to chamber width. That too is not overly common but common enough.
Thanks, I am aware of that but scoping the throat area indicates what I have described. If the headspacing is seriously off, the round case will still end up further rearward than what is normally expected exposing more of the throat to the combustion material.
That demonstration vid is exactly what I have described. It is not earth shaking but total erosion in that area leads to poor accuracy. Barrels wear out at the throat and can miss align a round.... that is known by about anyone familiar rifles.

I am not sure what we are debating presently? Every diagram you just posted shows the casing as far rearward as it will go when the round leaves the casing. If the head space is excessive, you simply expose more throat to the combustion gasses that erode the chamber over time...is that a false assumption on my part?

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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

I don't think there is a debate. Krag barrels were made at a pioneering-transitional time. Lots of things with an original Krag barrel are 'outside of' more modern SAAMI specifications.

Many Krag barrels look unpromising, but still shoot surprisingly good!

When do you give up on a barrel and for what reason?

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Parashooter
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by Parashooter »

reiver wrote: Wed Sep 14, 2022 3:35 pm. . . Every diagram you just posted shows the casing as far rearward as it will go when the round leaves the casing. If the head space is excessive, you simply expose more throat to the combustion gasses that erode the chamber over time...is that a false assumption on my part?
You're looking at the wrong end of the case. Consider that chamber pressure causes the front end to adhere to the chamber. With excess headspace the back end moves and the cases stretches at the transition between the solid base ("web") and the case body - but the front end is stuck to the chamber until pressure drops. We have to think of the front and back as moving independently to understand the dynamic.

I'm sure we can all agree throat erosion is bad - but I doubt strongly it is affected by headspace.

reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

Well, we agree to disagree then but thanks for all of the responses. Very informative material posted.

I am not giving up on this barrel simply loading long and beyond the rec. COAL. I am now out to 3.1350 without issues (also feeds thru the mag no prob). I will go no further but am not 'in contact' up front. It has greatly improved shot groups.
I agree about 'specs' too.... the gauges are excellent tools but not the final word. Especially in rimmed application. Still, am not overly pleased when a bolt 'falls' into battery with no pressure at all on a No Go. The Forster Field even has a bit of safety factor involved but they rec. you do not shoot the weapon if it so goes into battery. The old bolt will close on a Field gauge...said Forster and it is brand new. The NOS won't close on either. Very nice that.

I have little Krag experience buy have collected and owned/used all of the dif. Mosin sniper systems so get the nuances you are articulating...

I have loaded up some Speer 200 gn. Spitzer flat based rounds for tomorrow.... hoping they will print nicely.

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