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

I'm pondering two courses of action for my new-to-me SS Rem 700 7 mag.

Option 1: Leave it 7mm RM, and stretch out the throat to kiss a strategically-seated slippery bullet (Amax or 168 LRAB).

Option 2: With both 7-300 Winmag and 7 Mashburn dies on my shelf, a possible rechamber has its appeal.

I inquired with the good fellow in Chehalis about a rechamber to 7 Rogue, but he expressed concern that his reamer won't clean up a likely-sloppy 7 rem chamber. I'm inclined to believe him, so the question then begs - would your standard-issue 7-300 or 7 Mashburn reamer clean up the factory 7 rem chamber?

If yes, then does anyone know either someone with a reamer for loan or rent, or a smith with the reamer to do the work?

You may have to shorten the throat to kiss, just saying. And I'd shoot it first with a 168 Hybrid as that nose profile might get you close.

I can't speak to oversized factory chambers; but do know at least 2 people off the top of my head,who have punched Rem 700 rifles out to 7mm Mashburn.

One rifle has only been shot a little so far,but exhibits no brass issues and shoots accurately.

The other is owned by a guy who has had the rifle all over the place on BG hunting trips, including to Mexico last year for a record book Desert Sheep. So I guess it's working out pretty well.

He has not complained about any issues that I know of.

Ballistically, they are two peas in a pod.

The Mashburn has a cooler name and history, but there is nothing to recomend one over the other beyond that.

BTW, they are both a terrific upgrade and a good way to boost your rifle.

Vek if the logistics of the wildcat don't make sense for you,the 7RM is fine if you let the throat out for 160-162's. I have done it quite a bit years past and velocities seem to be in the 3100 fps range from 24" barrels. Pretty easy.

Every time one of these Mashburn threads pops up I start thinking. (always dangerous) And my thoughts always go to taking a 7RM case and blowing the shoulder out to the Ackley 40 degree configuration and throating it to take a 162AMax seated long.

I would tend to think this setup would be pretty close to the Mashburn velocity wise.

Also, before the Anti-Ackley faction gets their knickers in a twist, I did not pick the 40 degree idea so I could "overload" to excessive pressures.

I would use it mainly for the case trimming need benefits and a slight increase it powder capacity (i.e. 2%). Also in a pinch one could use 7RM factory ammo with this setup.

If you like tinkering and having something different go mashburn. If you don't like forming brass then I'd let throat out on 7mm remington

Been buying 280AI Nosler brass for some time...have grown lazy about forming brass...

I'd be tempted to let out the throat which won't have to be a lot for the 168 LRAB, and gander at 168g 7mmWB stats (if there are any) for a guideline of sorts

I say you do the 7-300 and sell those old 7mm Mashburn dies...

Alright, so who has a reamer for me to rent/borrow? Conversely, can you point me toward a smith with either reamer?

Thanks,

Sure plenty of smiths anxious to do the deed. Think Kevin Weaver in CO has a 7mm Mashburn, Smokepole used him I think.

If it is new to you, I'd clean hell out of the barrel, and load up either Retumbo or H1000 with 168 Berger Hybrids to see what you have. I quit trying to beat the 7mm Remington and just use it as is.

How soon do you need a reamer? I'm sitting on a new PT&G no throat reamer. But the first cuts will be in my new barrel. Bad news is, my barrel is still 2 or 3 months out. My reamer shipped in about 6 weeks if your looking to get your own.

4D reamer rentals had a reamer when I last checked in with them. I have not seen him here in a long while, but Dober (Mark Dobrenski) has or at least had a 7mm Mashburn Super chamber reamer.

VEK, fwiw, it might save you some hassle. But I'm on my 2nd 7mm Wby in two differ Remington 700's with 24" barrels.

I'm shooting book loads at Mashburn speeds.

Shooting 175's at 3,100 with 5 different powders.

150 LRAB's at 3,300 mv. RL 25

The 7mm Wby with its long neck and freebore make the difference.

I'd second that--the 7Bee is going to be the smartest way to fly--just cleanup chamber, lengthen throat as needed, and still be able to use standard 7RM in pinch. Pressure-tested loads available, headstamped brass, and easy velocity.

I'd be at least the third:)

mine is a 24 inch pipe model and it shoots 150 grain ballistic tips to 3220 with a bit of room to spare, 120 grain x to 3500, 140 grain x to 3330, and 150 swift scirroco to 3180.

personally I was expecting more snap than that but it is pretty consistant and is really more power than I really need.

to be honest I think that the 7mm weatherby might be faster than the mashburn if su35's velocities are correct for EVERY single 7mm weatherby out there.

79 the 150's are bit light but that's about right.Getting the velocity without having things screwed to the floorboards is what it's all about.

The 150 SS II is all copper I think and maybe a bit gummy.

One of our knowledgeable match shooters on here ran his Mashburn to about 3300 with the 150 BT from a Broughton barrel,but ran his ladder and found the accuracy node at about 3250. Recently he worked with the 168 Berger but I can't recall his velocity. He ended up exactly where I did with the 160-162 bullets at 75.5 H1000. I get 3200 with those bullets.



He described the cartridge as a "big easy going slob", not at all fussy and temperamental like some 7 mags can be.

We have not run anything lighter than 160 in any of ours back here.

i had a rem. 7mm mag. barrel opened up to the mashburn, no problems shoots fine.

Ed