Home Forums Reloading Big Game Rifles delta in COAL

Good afternoon.

I just measured my .375 H&H's COAL using Hornady OAL gauge for the first time. It came out to be 3.825" whereas Barnes reloading manual calls for COAL of 3.555". I understand the value in the manual is on the conservative side but I was surprised to find the delta of .270"! Does that sound right? I was going to back off .02" and start out with 3.805" for load development and incrementally reduce the length by .05".

Any expert opinion/advice welcome.

Regards,

You're talking about measuring to the ogive vs the tip

The measurement I listed above is the actual length from the tip (3.825") after measuring it with the OAL gauge.

Since this is the first time using this gauge I wanted to make sure the delta of .270" is somewhat in the usual range.

Regards,

The COAL of the cartridge is IIRC 3.6". Your 3.825" is 0.2" + over the max SAAMI cartridge lengh. This means little if your reloads will fit the magazine or if you plan on shooting it as a single shot as long as you work up the load.
The fact there is this much free bore in the throat is not a surprise. I've seen it run from almost nothing to "where the hll is the rifleing".

OAL is always bullet and firearm specific, never manual specific. Some manuals do not even list the OAL tested it is that unimportant.

Seat to what works best for you and your rifle and forget what the manuals say.

From Accurate Powder.

SPECIAL NOTE ON CARTRIDGE OVERALL LENGTH “COL”
It is important to note that the SAAMI “COL” values are for the firearms and ammunition manufacturers industry and must be seen as a
guideline only.
The individual reloader is free to adjust this dimension to suit their particular firearm-component-weapon combination.
This parameter is determined by various dimensions such as 1) magazine length (space), 2) freebore-lead dimensions of the barrel, 3)
ogive or profile of the projectile and 4) position of cannelure or crimp groove.

With monos in particular, OAL or distance off the lands means next to nothing in terms of what is going to produce accuracy.

I have solved more than fifty rifles with monos and some just are not touchy about seating depth. Some can be extremely touchy, +/- .005 has made the difference between dime size groups and 8 inch groups. I have some rifles that work best with the bullet touching or almost touching, at least one load the needs to be jammed, and a few that need to be out past .125 before the rifle shoots decently. Two apparently identical rifles may very well have very different seating depths with monos.

Can't say I've done 50, but 260 (120's), 270 (110's, 130's, 129's), 7-08 (120's), 30-06 (165's, 130's) loaded with the front of the first band at the case mouth were money.

Maybe my luck will run out with the 7Mag and 120's

Thanks so much for the replies folks.

The maximum length the magazine will accept is 3.720. I will start from there and back off by .02" increment to 3.560 to see which length might be work the best. Now just waiting for RL15 powder I have ordered to arrive.

Regards,

The thing to understand is that the critical dimension with monos is not magazine length, but rather distance off the lands.

Your plan may well work. But...if the rifle has a long throat and prefers it's bullets close to the lands you may be starting further off the lands than will work. I have found that the method requiring the least amount of bullets to find the OAL the rifle likes is to start .010 off the lands and work back in .010 increments until I see accuracy.

Picking magazine length as a starting point could well put OAL long enough that it may be too long for the chamber and have the bullet jammed into the lands, which could be dangerous.

MILES58.

Would you clarify what you mean by "mono"? Not sure what you mean by "mono" in the context of reloading.

Here is my logic as to why I am using the magazine length as my starting point. The measured COAL is 3.825" as mentioned above. However the maximum cartridge length the magazine will accept is only 3.720. Thus I figured there is no point of testing out any cartridge length >3.720" since I won't be able to use the magazine in hunting scenario.

A "mono" is simply a monometal bullet. Copper or guilding metal typically. Barnes, Nosler E-tpis, Hornady GMXs GSC customs are the most commn.

I assume by measured COAL what you mean is bolt face to lands measurement Which is neither COAL since you are not measuring a cartridge nor has much to do with it because of that fact.

COAL is a measurement that provides a reference point from which to work. .105 beyond magazine length is substantial throat. A fairly commonly used seating depth is .020-030 off the lands.

If the assumption is correct, then you have no choice but to start at 3.720 OAL and work back until you find acceptable accuracy. I work my loads up until I have consistent groups hopefully evenly distributed around point of aim and then I usually start at .010 off the lands and work back .010 at a time until I get the best I can. After that if more work is needed I will use small increments of powder weight change to find the middle of the best I can get. I like to search out that middle because I might be using the load at 75 degrees or 20 below zero.

If working back from 3.720 is not producing accuracy your options are to switch bullet weights, switch shapes (TSX VS TTSX for instance) switch to a different bullet like an E-Tip or GMX. My experience is that seating depth with monos tends to be specific with a given bullet and rifle and powder does not seem to matter so much. You can see the right seating depth fail to produce accuracy at "normal" speed, but very nice accuracy at substantially reduced velocity however. I have seen that happen with a few rifles. The first time I saw that was with an '06 that would not shoot a Barnes 130 TSX accurately above 2950 FPS with 6-8 different powders. That same rifle not only shoots 130 grain TTSXs into small groups at speeds from 2950 through 3350, they also stay at the same point of aim.

YHC, here is my 2 cents worth...If I had that much freebore in the throat and had to seat my bullets that much shorter to fit a magazine I would have the barrel set back and rethroated. Any competent gunsmith can do it fairly quickly and painlessly.
Please trust me on this, it will save you many bullets and much powder and even leave more hair in your head at the end of the day. I would match the throat to the magazine length. Rarely have I found a bullet that will not shoot whether it be monos or cup and core that needed to be seated at more than .015 -.020 off the lands. My personal 375 likes most loads at .005 off the lands and fits the magazine just fine.

Bill

Thanks for the explanation and advice everyone. Very helpful indeed.

Regards,

YHC...FWIW; I have SEVERAL rifles with [chamber] COAL longer than the magazine length. However, at least two rounds will fit into and feed from the magazine at the longer COAL length with the bolt closed.
With one round chambered and two in the mag, shouldn't three be enough?
WILL.

Thanks for the reply Will. Theoretically one bullet should be enough with "one shot, one kill". I have killed plenty of animals with a single shot from small roe deer in Germany to Kodiak brown bear. However I do not like to hunt with a round in chamber and I prefer having a full magazine just in case things do not go as planned.

Regards,