Home Forums Hunting & Shooting Custom Rifles & Wildcats Rechamber to Mashburn or 7-300WM

DD: Basically what Keith said.

IME, I have dicked around with enough barrels and various throats with longish throats to know some will shoot with substantial jump to the lands (if tolerances are kept tight),and some are on the sloppy side and won't. I have had factory rifles that I had to lengthen mag boxes for longer OAL so I could get closer,and then they shot.

Just as an example, I have never shot a 340 Weatherby that was not accurate and grouped well. But not all 300 Weatherby's did. 340's are not free bored,at least those I helped load for were not. OTOH, 300's are.

In any event it was not a condition I wanted to take a chance on in a custom rifle costing a few thousand dollars.

When designing a Weatherby reamer with short freebore, cut the neck length short enough to where factory ammo will not chamber, did this on a 257 Weatherby so that I could reform 264 WM and 7 Mag cases.

Again, .0003-.0005 throat dia on freebore will work to keep the bullet straight. A throat that is .003 over bullet dia is a disaster to accuracy....take that to the bank.

My 7/300 is easy, I just run a 300 WM thru a 7 mag die to resize the neck and after the first firing resize with a Redding bushing die in 300 win mag die with the bushing changed out to. 7 mm. The first round is just as accurate as the second because when I resize to 7 mm I leave a little crush fit in the neck for a slightly tighter fit

I run 140s to 3300 with no problem with 7828 and Winchester Brass

Steve I used to form your case the same way wile playing around at the loading bench but never chambered for it.

RinB on here had a pal who did,and we used to talk a lot about it.Obviously they are the same/same with the Mashburn but a shorter neck.

Bob,
Same same.The 7mm Practical.
http://www.ballisticstudies.com/Knowledgebase/7mm+Practical.html
The fact that you can buy 7mm Mashburn S bushing dies off the shelf at Redding...although it took awhile to get them.....makes it pretty easy.

dave

Dave yes; I had read about the Practical.Like i said I was forming that case while goofing around the loading bench years back.

There isn't much to choose between it and the Mashburn. The author distinguishing between the two on the basis that the Mashburn was originally formed from 300H&H brass is somewhat true, but has not been so since Bob Hagel started using 300 WIN Mag brass to form Mashburn brass 30+ years ago.

In terms of performance, they are the same.Both cases hold more powder than a 7 Rem Mag.The Mashburn neck is longer if that's important to some people.

When we ordered Mashburn dies from Redding they did not make any...my FL dies were made from scratch with brass fired in my rifle. I did not know they made the S Bushing dies now. They must have added them to the line.

If I can make a suggestion, if you order Mashburn dies from Redding have a candid conversation with them and be VERY specific about neck diameter.

I bought a set from them a couple years back. They gave me the choice of a standard FL sizer or the first Bushing die off the line. I thought I was saving a few bucks and went with the standard FL sizer. Bad decision.

The problem? The sizer die sans expander ball produced an outside neck diameter of 0.292". Absolutely stupid. That's a whole 2 whole thou larger than my 6.5X55 die, and I run a .290 bushing in my 260 Rem competition Redding sizer die. After the case is run into the neck of the sizer die, the expander ball has to neck it back up 20 thou. Yup, you read that right.

Redding were lazy or didn't think through specifications. Nothing like having to reef upwards on the press handle to get the expander ball back through the case neck.

I called Redding about it and they didn't care. Suggested I send the sizer die out to be reamed so it was usable. Yeah, nice...pay $175 for custom dies and need to have them fixed by a third party.

My gunsmith had to anneal the die to soften it, run in a .308 throater, then reharden it. Using WW 300 Win brass, that takes the neck down about 6 thou and necks it back up 4 on the expander ball. That's plenty to ensure you can use about any brand of brass, and works the brass neck no more than necessary. Makes straighter ammo as well.

If I was to have Redding make "custom" Mashburn dies again, I would be specifying a .308" neck diameter sans expander ball. If they wouldn't, I would go bushing dies or go somewhere else.

A simple solution to that problem would be to totally ditch the expander ball.Have the neck of the die counterbored out to accept a Wilson/Redding bushing.This way you could size the neck to whatever you wanted.Then buy a cheep hand decapper.
Problem solved.
My smith had a 7mm Mashburn die from RCBS.
I had to borrow it for awhile and it worked fine.
I loose the expander ball in every round I get serious about everytime.
I get much less runout that way.

dave

Agreed, and I normally do so as well. But if the diameter is correct and you use an expander ball to bump back up a thou or two it doesn't result in less straight ammo. If you are talking your typical die which necks down a bunch more than necessary of course you are correct.

To have the die bored out you still need to have it annealed. The die from the factory is way too hard to be able to counterbore or ream.

Much simpler to go bushing or have the diameter specified from the get go. With that die, if you just ditched the expander ball you could also just use 6.5 bullets!

Do you mind sharing how much 7828 to get there? Does it seem to you like there is room for more powder and speed with that load?

Rick I did not know about any of this....will check mine but can't recall a problem.....mmmmm

One of the problems with a 7mm Rem Mag AI, not that it is a problem, is that you still have a very short neck length.
One of the very things that 300 Win mags and 7mm Rem mags are noted for.
Longish necks and 30 degree shoulders rule.
Especially when lobbing heavy per caliber bullets..
And Parker O. Ackley is my hero by the way..
A 300 Win mag case stroked in a 7mm Mashburn Die is closer to final net shape than blowing a 7mm RM AI.
Ammo.
I see the....if I loose ammo thing about wildcats alot....
If you loose your ammo.
Your pretty much screwed no matter what kind of gun you have.
Putting some different kind of ammo in your rifle on an important hunt would be just like usuing someone elses rifle.
Might was well just start over....


dave

Dave7mm,

I am going to test this in my own 7mm/300 WinMag soon, but just like I have fired 300Win and 300 H&H in a 300WBY, I can see absolutely no reason why, with headspacing being done at the forward edge of the belt, that one could not safely fire a plain vanilla 7mm RemMAg, 7mm WBY, 7x61 Sharpe and Harte or a 7mm Mashburn Super in a 7mm/300 WinMag chamber. The only downside to doing so would be pretty low and maybe non magnum velocities since one would be firing what amounts to a pretty mild powder charge in the larger case. Chamber/FINAL case dimension is what determines peak pressure and thus velocity.

Nope, it is my old, Model 70 XTR 7mm Rem Mag. Been sitting in the safe collecting dust for a few years since I got the 7mm WSM. Figure I might as well do something good with it. Forming 7 MSM cases from 300 Win Mag is a cinch compared to 375 to 35 Newton..

Here are a couple of reformed cases for the 7mm MSM.. I had some old R-P 300 Win Mag cases laying around from my old 300 Win Mag. I merely ran them up into the FL 7mm MSM dies and voila...

Here is the 7mm MSM next to the 7mm Rem Mag.



I couldn't help myself and loaded up a few more dummies..



The 160 AB is seated right at 3.600 COAL.. The 162 AMAX went a little longer at the same die setting.

Also, the case isn't fireformed yet. It won't be drastic, but the little bit of taper in the 300 Win case will get blown out during fireforming, so it'll pick up a little more space there as well.

I also swapped over the mag box in my old Model 70 7mm Rem Mag. Well, technically I knocked out the spacer to make room for a 300 H&H follower. Works very slick now. I also fitted a 300 Wby bolt stop to allow my bolt to come back full stroke.. Really easy stuff.



Nothing special about the rifle, just an old M70 XTR Sporter. I through it in a B&C Medalist and cerracoated it as well.

Well, here are some results from the fireform loads.. Overall, I could just about hunt happily with the fireform loads the way they sit now. A little seating on the 140 AB and it would be good to go!

Here is the 139 grain Hornady, Hornady Case, 3.520" COAL and CCI250 primer.



Speeds ran pretty much around 3200 from what I could tell.



The 140 AB's were a COAL of 3.575". Everything else was the same..



They ran about 25FPS faster than the Hornady's..



What I was surprised about the was the POI difference. Both groups were shot using the center bull. The 139 SPBT was zeroed about 2" high, while the AB's went high and to the right. Not a big deal, but it was drastic for two bullets that differ about 1 grain!



At 3200 with a 140, this thing is just loafing along, even with IMR4350 which is a big on the fast side, but everything worked well. Cases chambered tightly with a good crush fit, but they extracted with no resistance at all..

The rifle shoots well and it's pretty gentle. I just put an old M8 4X on it for now. Not sure what I will put on it for hunting, maybe nothing different.. Who knows..



Either way, for a 120 bucks for the rechamber, I am calling it a success so far. Doesn't seem to be overly fussy. Once I get a few more empty cases, I'll load them up with some 160 AB's and see what happens..

" Doesn't seem to be overly fussy "

Is the term that everyone I know that has one says after they play with it.
Even for alittle bit...


dave

Seems like it. Can't wait to get it out tomorrow. Got some 160's loaded with H1000. Should be a nice morning.

Can you kiss lands with the 162 and fit in the magazine?

Yes. You can with mine. It's a wildcat and reamers vary.