Krag 30/40 and accuracy vs. chamber/throat

Ammunition, reloading, shooting, etc
reiver
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Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

The accuracy to date, iron sights, is OK but I expect better given the bore condition. That does not equal the throat or headspace tho.
The headspace was off a bit and I fixed that with a NOS bolt...like our Mosins headspace is set by the rim, as you know, and the old bolt was worn.
I measured the chamber/throat too and, like many old rifles, it is no longer what it once was. The max coal recommended for the 30/40 is 3.089....I measured my chamber with this very handy Hornady tool (make my own brass-drill/tap) and extended the COAL out to 3.1050 and gave myself a .10 leeway. I've fired 3 rounds and not hardly any residue on the cases indicating a nicer 'fit'... so I'll try the 150/168/180 gn FMJ at that length and see this week.
Throats and leade's grow/recede and older rifles really need a chamber measured.
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reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

Well good results today...just iron sights. Moving the round length beyond the max rec. coal of 3.089 to 3.1050 paid off.
When reloading just below 3.089 with 150 gn rounds and H 335 @ 35 grains I was at about 3 MOA at 100 yards.... terrible for the quality of the bore that has very crisp rifling.
I know that 150 gn .308 in a 1 in 10 inch twist is not the best but I expected better than that.
After realizing the throat/lead was worn I went beyond the rec. coal but gave myself a .10 safety factor ( I may go a bit longer). These rounds feed properly in the mag at 3.105 btw.
The 150 grains round tightened up to about 1.75 MOA but here are the 168 FMHTB Hornady and the 180 FMJ flat base interlock results.
The flat based rounds, in my experience, work best in older worn throats...and they did so here. I used IMR 4064 in the 180's at .36.1 gns.
This is benched, lead sled as I was testing loads and not myself.
The two spent casings show the difference in powder residue...the over COAL is clean...the other you can see for yourself. COAL is a moving target so measure and don't be afraid to experiment.
I think a 200 gn round, flat based would be perfect.
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FredC
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by FredC »

I understand the principle of getting the full diameter of the slug near the rifling is thought to improve accuracy. Krags have traditionally done well with greater distances, not sure why. Br has shot some impressive groups with 110 round nose bullets that must jump a bunch before engaging the rifling. Down side was they did not feed and had to be singly loaded. If all your groups in the photos are at 100 yards, your groups are impressive also.
What does COAL stand for, I think it has something to do with the effective length of the loaded cartridge. Will all these feed through your magazine? Some cartridges that vary too much from the original 220 grain round nose do not do well in some Krags and others will feed 150 grain spitzers fairly well.

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

Post by reiver »

COAL is the Cartridge Over All Length and for the 30/40 it is listed as 3.089 for reloading as the maximum length. I've never seen a blue print of the original Krag chamber, or the slightly modified later one (shortened) but all of the reloading material I have states the same COAL.
My barrel rifling was, and is, excellent but the throat was worn by a sloppy head spacing.
The headspace was fixed, thankfully, by a NOS bolt. The tool shown above is very good at measuring the actual length of your chamber at the throat and lead.
By extending the COAL to 3.1050 (or a tad longer) I am simply moving the round where it is intended to be.... throats wear and when they do they 'grow'.
They can get to a point where the only solution is to remove the barrel and replace it or re ream. Thankfully not there yet.
A 1 in 10 twist likes heavier rounds and so far the 180 GN FMJ Spitzer flat base has worked best...much better than the 168 GN FMJ Spitzer boat tail. A little wear in the throat likes flat based rounds too.
The longer rounds feed fine in the magazine. Not sure how much longer I could go and still have that function properly tho.
This was shot from a lead sled as I wasn't testing myself but the loads alone.
Reloading and finding that sweet spot is half the fun for me.

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

Post by butlersrangers »

I believe the throat (or 'leade'), in front of U.S. Krag barrel-chambers, was rather generous from the start to accommodate 230 & 220 grain round-nosed projectiles.
Also, this area of the barrel wasn't helped any by some of the early propellants.

I suspect generous 'headspace' plays more of a role in stretching Brass than it contributes to barrel throat erosion.

The 3.089" maximum 'Over All Cartridge Length' goes back to the origin of the .30-40 Army cartridge and appears related to magazine dimensions.

IIRC - There was special Match Ammo made for the Krag and 1903 Springfield, in the early 1900's, that was directly loaded into the chamber.
These Match Rounds were too long to feed through Krag and 1903 Springfield magazines. The longer rounds were used during 800, 900, and 1,000 yard 'slow-fire' matches.
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FredC
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by FredC »

OK, so it is overall length measured from back of the rim to the front of the projectile. I thought it might be to the first part of the bullet's full diameter .308 in this case. I know one of Weatherby's old tricks was to increase the free bore length so the bullet would be moving along at a pretty good clip before it engaged the rifling. That was to keep the almost insane pressures under control. If the free bore was fairly tight not much gas could escape ahead of the bullet, also the bullet would be more likely to be centered when it hit the riffling. I think I see .31 on the drawing the Br provided. Then you have tolerance and wear on top of that. So that is probably looser than new barrels today.
Finding a sweet spot for each Krag takes some time, looks like you are well on the way. A few years ago, another member went to lengths finding which primers gave the best accuracy. On primers you would think the brand that gave the most consistent ignition would be best for every Krag and every rifle for that matter, but that is a little hard to prove.

One word of caution, I suppose in experimenting one could start loading rounds so long they would not feed or even go though the magazine. At some point you might be able to get so long that the bullet engages the rifling when chambered, that could lead to pressure spikes if the bullet has to overcome inertial and enter the rifling in the same instant.

Please keep us informed as you continue down this road.

todd444
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by todd444 »

WHAT IS THIS HEADSPACE YOU ARE TALKING ABOUT? :lol: :lol: :lol:


i use .311" 165gr Ranch Dogs and the throat is long that you can't use the RD. so i load it up to the crimp groove and i "forget" anything related to the throat and headspace. i killed 9 or 10 deer and my son has killed 5 or 6 of them. my son's furthest shot was 173 yards(laser range finder thingy) and i shot one at about 140-150 yards. mostly the deer are shot at 30-50 yards.
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reiver
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by reiver »

BR, great post and schematics...and THAT is a lead sled.

Todd, did you slug your barrel before using the .311's or just went that route? A worn bore, worn evenly, will still shoot pretty accurately. I've used .312's in Mosins after slugging them and they did well.

If the bore is still closer to .308 and you are shooting .311's then your CUP will certainly climb and you would just be wearing the bore out quicker. I shoot way too much to go oversized without any proper check. Are you shooting handloaded lead or copper clad?

Fred, yup, that is COAL. A little freebore in a single bolt lug rifle is always my plan. The 3.1050 to 3.1080 work fine in the mag.

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

Post by Parashooter »

This sketch might help with terminology. ("Leade" is sometimes spelled "lede". Writing "lead" for this element can get confusing.)
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butlersrangers
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Re: Krag 30/40 and accuracy vs. chamber/throat

Post by butlersrangers »

Thanks 'Parashooter', I corrected my post to "leade".

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