375 Weatherby Magnum cast bullets free bore

[rp85]

good evening;

Not sure I’m in the right forum for my question other than it’s about shooting cast bullets.

Purchase a custom 375 Weatherby Magnum rifle several weeks ago. Original owner passed away many years ago and his brother was selling the rifle. R\H Sako action converted to L\H, 26” med weight barrel, total weight of rifle is 10+ pounds. Brother shot the rifle and his only comment was recoil “will hurt you.” Have purchased 100 375 H&H brass to fire form to 375 Weatherby.

Plans are to shoot only cast bullets in this rifle. Rifle shooting 1” or less with cast bullets at 100 yrds. Became concerned having to seat the bullets, Lee 375-250 & Lyman 375449, at start of ogive curve on bullet’s nose to close the bolt.

Asked gunsmith to check rifle because of bullet length required to close bolt. Rifle has no free bore at all. Gunsmith express concern shooting Weatherby jacketed bullets ammo in this rifle. Said I should never shoot Weatherby loaded ammo in this rifle because the risk of extreme high pressure with no free bore in the barrel. Shooting only cast bullets saved me from a serious situation with high pressure. Ordered a .373 throat reamer to bring barrel into Weatherby specs.

Anyone shoot cast bullets in a 375 Weatherby Magnum with factory free bore spec? Like accuracy with cast bullets but do not like the idea of proof testing the rifle every time I shoot the rifle. Thx for any input.

rp

Update: gunsmith messed up, maybe. went from "0" free bore to .410"

request for cast bullet speed. arsenal mold, 283 gas check ( lyman 375449) clone. chronograph 12' from barrel;

15 grains of Red Dot = 1400fps\ 3 shot group size .686"... very little recoil

34 grains imr 4198 = 1790fps\ 3 shot group size 1.250"... recoil sim to .243 win

35 grains imr 3031 = 1645fps\ 3 shoot group size .526...recoil sim to .243win

rifle purchased to shoot only cast bullets. accuracy impressive with such a big caliber. the red dot groups are 4" lower than groups with imr3031.
plans are to use red dot or imr 3031.

[PositiveCaster]

Clearly a custom rebarrel it should have been marked ‘short throat’. I have a custom .257 WBY with a short throat, max loads are 4-6 grains lower than in my other .257s. Excess pressure/velocity could be the reason your .375 recoiled so badly for your brother…

But since it shoots so well now, if all you intend to shoot is cast why would you lengthen the throat and risk ruining that accuracy? Cast bullet data is nowhere near SAAMI maximum pressure. If it’s not broke…




.

[gwpercle]

Clearly a custom rebarrel it should have been marked ‘short throat’. I have a custom .257 WBY with a short throat, max loads are 4-6 grains lower than in my other .257s. Excess pressure/velocity could be the reason your .375 recoiled so badly for your brother…

But since it shoots so well now, if all you intend to shoot is cast why would you lengthen the throat and risk ruining that accuracy? Cast bullet data is nowhere near SAAMI maximum pressure. If it’s not broke…




.

My thoughts also ... dedicated to shooting lead ... shooting 1" or Less with cast ... it isn't broke ...so why fix it .

Might have the gunsmith mark the barrel with a warning for the next owner ... but that's about as far as I would go .
Gary

[rp85]

good evening;

thanks for input.

seated cast bullets, Lee 375-250 & Lyman 375 cast, case mouth extends into the ogive of bullets. only way I'm able to close bolt. barely enough to hold bullet in neck of case. this rifle has no free bore at all. spec is .373 free bore.

have ordered a 4d throat reamer will ask gunsmith to cut throat with .225" free bore. that length is based on a master dummy round long enough to bump into rifling, enough of bullet below ogive of bullet and still able to close bolt.

gunsmith expressed concern on lack of free bore with caliber. Weatherby magnums need free bore to help with pressure. His concern is someday this rifle will pass on and who ever has the rifle they will have pressure issues with factory ammo.

thanks again for input.

rp

[gwpercle]

good evening;

thanks for input.

seated cast bullets, Lee 375-250 & Lyman 375 cast, case mouth extends into the ogive of bullets. only way I'm able to close bolt. barely enough to hold bullet in neck of case. this rifle has no free bore at all. spec is .373 free bore.

have ordered a 4d throat reamer will ask gunsmith to cut throat with .225" free bore. that length is based on a master dummy round long enough to bump into rifling, enough of bullet below ogive of bullet and still able to close bolt.

gunsmith expressed concern on lack of free bore with caliber. Weatherby magnums need free bore to help with pressure. His concern is someday this rifle will pass on and who ever has the rifle they will have pressure issues with factory ammo.

thanks again for input.

rp

Yes ... throating it to accept your cast boolit load is needed ... but throating it so deep as to cause an accurate shooting rifle to not shoot accurately ...just because someday ...some other person may shoot factory loads ... I don't know ... screwing up a good shooting rifle for some future thing that might not happen ...
I would Mark a warning on the barrel , right below the caliber and keep the short throat for shooting your boolits .
Gary

[bobthenailer]

A friend has a 378 WB and it shoots jacketed pretty good! but each shot is worse than the last, we found that shooting from a benchrest that is about 5' high so you can shoot the gun standing up helps alot!

the ideal senario for cast bullets is the bullet nose just touches the rifleing but still works in the action. long free bore and cast dont mix from my experance

[Nobade]

Your first post said you ordered a .373" throating reamer. I hope that is not the case, you want a .376" throating reamer then run it in as far as you think to fit your round. Weatherby spec might be .373" long, but not the diameter. Hopefully your gunsmith knows what he is doing.

[wmitty]

I had wondered about this dimension also. I assume you are saying the throat will be cut to .225” in length from case mouth to start of the leade. It almost takes a sketch with arrows pointing out the various areas being described to get everyone on the same page. Would you mind telling us the diameter of the throat you plan to have reamed? Groove diameter or larger than groove diameter?

[rp85]

thx for input.

rifle bought to shoot only cast bullets. per gunsmith, a Weatherby caliber rifle shooting Weatherby factory ammo you will have very high pressure if there is no free bore. This rifle has no free bore at all. if you have a factory Weatherby round and you extend the length .002" you can't close the bolt.

from gunsmith the number ".373" (Weatherby spec for free bore in this caliber) is to lengthen throat of barrel. goal is take a barrel without any free bore and some create some free bore. as of now, in order to closed the bold with cast bullet the mouth of case extend into the ogive of bullet. nose of bullet barely extends from the mouth of case. cases are trimmed to factory spec.

have a dummy round with Lyman 375449 and use its length to determine how much free bore for barrel. looks like .200-.225" will be added for free bore. it will still be a "short chambered" 375 Weatherby because it does not meet Weatherby's spec for free bore in this caliber.

thx again for input.