Sizing to the throat, how snug?

[RickinTN]

Hello all,
A friend and I are working with his Windchester 94 Big Bore in ..375 Winchester. The outside diameter of the throat in his rifle measures .3803" to .3804". We are to the point of needing a sizer. I intend to size to the throat of the rifle and am wondering how snug do you go? I'm a bit nervous about trying to size to .380" in that the rifle has a long parallel section of the throat and the ammunition would have to be very straight to chamber not to mention if we ended up with a harder alloy it would size larger and then may not chamber at all. So, the question is, when sizing to the throat in such a rifle how snug do you go? .379?, .3795?. I'm curious to hear what your opinions and experiences are.
Thanks in advance, and take care,
Rick

[DougGuy]

A lot of that depends on the antimony in the mix and how long it is going to sit on a shelf after sizing. Cast boolits will grow, I try and size cylinder throats .0005" ~ .0008" over boolit diameter for 35 and 45 caliber cylinders, which would likely work for your application but longer boolits tend to grow more than shorter ones of the same caliber so the longer the parallel sides, the potential for more growth maybe?

It is not unusual at all for a 400gr boolit for 480 Ruger grow over .001" and the even more for heavyweights in .500 caliber, not unusual to see .0015" in one of these after sitting a few months.

Sizing to .3795" might be the ticket but you also may not even be able to tell the difference between .379" and .3795" downrange.

[Outpost75]

DougGuy is spot-on. I have also found that with ternary Pb-Sb-Sn alloys, if extrusion ratio of as- cast down to throat size exceeds 0.5% of bullet diameter, you can expect more growth in sized bullet diameter through recrystallzation of the cold-worked surface as the internal strain is relieved. This is less-so with binary Sb-Sn alloys and bullets cast from molds very close to desired diameter which require less than 0.001" in sizing.

[popper]

You probably need a 0.001" clearance. I don't have anything to measure 1/2 thous. but IIMHO the 'growth' is from alloy springback. Get a sizer on the small size and you can hone out if too small - might want to get a couple. I have a 401 Lee that worked until I mistakenly cast pure/tin, then honed it out - another mistake - too large for COWW. WD or AC will make a difference also. Larger dia. boolits should grow absolute more but longer boolits can't cause more growth, unless they shrink in length - or get stretched when sizing.

[DougGuy]

You probably need a 0.001" clearance. Larger dia. boolits should grow absolute more but longer boolits can't cause more growth, unless they shrink in length.

If an alloy "age hardens" which many do, I think they contract along the length and being the length is a much greater distance than the diameter, as they harden the push the diameter outward due to contraction along the length. That's only my WAG as to how this happens and why longer boolits seem to exhibit more growth measured across their diameter than shorter lighter boolits of the same caliber. No proof behind it other than that.


I intend to size to the throat of the rifle and am wondering how snug do you go?
Rick

As mentioned earlier, a lot of this depends on your alloy. With the pressures built on ignition, every cartridge tries to shove the bottom of the boolit forward and in this initial shove, overcoming the force of inertia to start the boolit moving will cause the diameter of the boolit to "bump up" or swage outward until either the case walls or the cylinder throat arrests this growth once it has bumped up to take up all the available space there is for it to take up.

Generally, more pressure = more swaging, softer alloy = more swaging, harder alloy = more resistance to swaging so there comes a point where you can size to .377" and your boolit will still fill the throat in the barrel if there is enough pressure behind it, AND/OR if the alloy is soft enough to be swaged by the amount of pressure your load develops. Harder alloys might not swage nearly enough to seal the boolit in the throat and you have gas cutting and a tremendous amount of leading.

I am sure you will find a combo that works for your buddy's Winchester. I would think with harder alloys you would want to be sized closer to throat diameter after springback and softer alloys wouldn't matter if they were as much as .002" under throat diameter if in fact they are bumping up to throat diameter as they enter the leade in to the rifling. So if your harder alloy comes out of the sizing die at .3795" and your softer alloy sized to .378" it may not matter a bit how well it handles the softer boolits.

[runfiverun]

I size to 379 for my 375 Winchester.
water dropped ww's cut with stuff that's softer.
they can grow all they want they'll still chamber and shoot just fine.

[RickinTN]

Thanks for all the knowledgeable replies. We will most likely stick to clip-on wheel weight or even softer alloys as I'm thinking the rifle will spend most of it's life loaded as a light to moderate 38-55. It would be good to leave a little room in case we were to try a harder alloy, such as Lyman number 2, of which we mixed about 100 pounds of yesterday. I have had 30 caliber bullets "grow" .0002 to .0004" over time but I have no experience with big long bullets. I would have expected them to grow more in diameter than the smaller bullets. I think we'll probably shoot for sizing clip-on wheel weight bullets just a tad over .379, and doing so leaving enough room for bullet growth or for harder alloys to size larger.
Thanks for all your help,
Rick

[Wayne Smith]

Rick, how thick is your brass? Need to leave enough room for the neck to expand and release the boolit, too.

[RickinTN]

Wayne,
That is certainly a valid consideration as well. With standard .375 brass and a .379 bullet we will have .003" left for neck expansion to release the bullet. The chamber is cut for standard length 38-55 brass, or 2.095". We may at some point in time try some 38-55 brass. I understand it is thinner in the neck than .375 brass but it would help fill the .075" void in the chamber between the 2.020" 375 brass and the 2.095" chamber.
Thanks,
Rick

[TomAM]

I size to .380".

Something to consider with this cartridge is that your chambers are cut to accept a case of at lease 2.08" length, even though 375 Win brass max length is 2.02".

The chamber length that Winchester submitted to SAAMI for cartridge standardization is the same as Starline's shorter 38-55 case, and I have encountered only one model 94 which would not easily accept the longer 2.125" brass.

I have gotten much better accuracy using this brass, which greatly reduces the length of .402" diameter tube that the bullet must otherwise tumble through before reaching the throat.

And you don't have to pay "collector's item" price for the brass.

[RickinTN]

Hello There Tom,
His throat will accept the standard 38-55 brass from Starline, but not the long brass. The chamber length in his rifle is 2.095", so just a little clearance for standard 38-55 brass. The .402"neck diameter of your chamber is consistent with his. I've been eyeing your 235 grain bullet and comparing it's dimensions to the throat in his rifle and have concluded that the chambering of his rifle is a very close match for the chambering of yours. I'm sure we'll be in touch soon to order a mold. We do have to decide if we want the crimp groove placement for 375 brass or 38-55 brass.
Thanks, and take care,
Rick

[TomAM]

You should check out my #38-200AG.

#38-235A has the crimp located for 375 brass, and 200AG is for 38-55 brass.
I use 2.125" brass in mine, and my nephew's 94 takes the 2.08" brass.
In both of our rifles, the nose of #38-200AG just starts to be engraved by the leade upon chambering.
So, at least in our two guns the distance between the chamber's end and the leade are the same, making 200AG a great fit for both.

Accuracy is excellent for both of us with this bullet, and recoil is significantly less. And unless hunting mammoths, the "greater" penetration of heavyweights is just not needed.

[RickinTN]

I've studied the 235 but haven't looked at the 200. Lower recoil as well as using a little less lead would both be welcome. The most he would ever use the rifle for outside of paper punching or shooting a gong would be one of our 100 to maybe 200lb whitetails on the hoof. As a friend of mine says, "It's a rare occasion we have any dinosaurs pass through middle Tennessee!".
Thanks for the input!
Rick

[cainttype]

I have not had a 375 Win firearm that does not accept 38-55 brass, and I currently have 4.
I would only use 375 Win brass if I were loading top-end jacketed and was worried about the "weaker brass", but I'm not shooting Js... and I'm not worried at all about the brass. :smile:
I would size .0001 under throat and use 38-55 brass in your situation. I'd treat the rifle as a 38-55 (which is great in it's own right) and live happily ever after.
There is a great variety of mould designs out there for this diameter. I'd consider anything under 240 gr as a lightweight, 240-275 as mid-weight, and 275+ as heavies... I like mid-to-heavies, in general, but even lightweights like the 235s are serious medicine from the .375W and 38-55s.