Barrel length for the 7MMs? New build?

[Tangodown911]

I have been reading like crazy and searching everything I could find about the 7mags and 7wsms. I'm really liking the 7SAUM for it's increased barrel life over the 7wsm. From what I gather it's possible to get about twice the barrel life with the 7SAUM over the WSM. The 7s seem to have the upper hand with BC and lighter recoil compared to the 300mag and WSMs...basically all the .30 options. And still be able to deliver sufficient energy on target at over 1k. I will be using a 591 for the action and going with either a bartlein or krieger barrel in a HTG. I'm not one for the long actions... Fine for others just I prefer to keep it a short action.

I plan to shoot the 162Amax and the Berger 180VLDs. I'm hoping to keep the bergers at 2900fps or better. What about barrel length, contour, and twist?

I have a 9 twist in mind and want nothing lighter than a rem. varmint contour or heavier than a medium Palma... I think they are rather close in weight so that may be a decision like 6 of one and a half dozen of the other. Realistically what are the limits of the barrel before he groups will start to open considering the lighter contour and the higher heat this round will generate. In over words if it's a one hole gun and load with 5 shots, how many more will the barrel withstand before it starts to give.

I'm think 24-27" on the barrel. But as you can see I'm not certain. The 7s are all new to me and I'm lookin for advice from the 7mm guys as to what has been working for you. What are your thoughts?

 

[bailey1474]

Re: Barrel length for the 7MMs? New build?

I like a 25" bbl. Not sure why but that is just what I like. Guess 26" is too long and 24" is too short. I think you will reach your goals w/a 25" or 26" bbl.

 

[head2h2o]

Re: Barrel length for the 7MMs? New build?

GAP is building a 7SAUM for me right now. I decided to go with a 26" barrel for the finished length that was 1 in 8.7 twist. It will be a Bartlein on a 591. As for the life of it, many factors play into that, but I can tell you that one of the local guys here got about 2500-3000 rounds out of a 7WSM, so I am not sure that the 7SAUM is good for 2x as much barrel life as the WSM. I plan on shooting the 180's out to a 1000+. I have a 26" factory savage in 7mmRM that is pushing the 160 accubonds down a 1 in 9 twist barrel at 3000fps with very impressive accuracy.

 

[TEAMSENDIT]

Re: Barrel length for the 7MMs? New build?

if you want 2900fps i would recommend a 28" that way you won't have to push it as hard to get there. 9 twist all the way, i prefer the palma contours over the rem but not a big deal.

I can damn near guarentee you won't get 2x barrel life of wsm it will be better and you do see more benchrest and f class guys use saum because it has longer neck shorter case=more efficient and easier on your throat.

I can't say to much though because i am about to build a 7/300 mag and i am hoping to push the 180's to 3100fps.

 

[Gruff]

Re: Barrel length for the 7MMs? New build?

My 7mm RSAUM has a 29" Hart heavy varmint contour 9" twist barrel. It sits in a McM A2 stock and is topped off with a Sightron SIII 6-24x50mm. It weighs about 22 lbs. My loads push a 180 gr Berger @ 3100+ fps mv. From my 600 yard zero, it takes only 11 minutes of elevation to reach 1k. With over 1400 ft/lbs of energy, it craters A36 steel at 1k. Ballistics program says I'd lose about 150 fps mv with a 26" barrel.

My 700P in 7mm-08 has a 26" factory varmint contour 9.25" twist barrel. It has a Sightron SII 6-24x42mm scope and weighs about 12 lbs. My loads push a 175 gr SMK @ 2750 fps (the 175s allow for mag length loads). From 100 yd zero, it takes 31 minutes of elevation to reach 1k and still has over 800 ft/lbs of energy when it gets there.

 

[Tangodown911]

Re: Barrel length for the 7MMs? New build?

Thanks for the responses. I'm leaning towards 27" and going with a medium palma contour. Still not sure how many rounds that contour will handle without heating up and causing accuracy to drop off.

Head2h2o...8.7 twist is interesting. Is that barrel a Bartlein?

 

[Bacarrat]

Re: Barrel length for the 7MMs? New build?

My 25" WSM is hitting 3005FPS with the 180s. First barrel I got 3300 rounds out of the barrel before I installed the a 8.7 twist Rock. I was running moly at the time and it could have probably gone for the rebarrel a couple of hundred rounds earlier. So let's call it good for 3000 rounds. I highly doubt you will get anywhere close to 6k rounds out of the barrel with a SAUM. I would be shocked if a SAUM can even hit 4K rounds. I am sticking with the WSM. Remington brass isn't all that great, and even if you resized Nosler 300 brass, who knows how long it will last. My experience with Nosler stuff hasn't been all that great.

 

[Tangodown911]

Re: Barrel length for the 7MMs? New build?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bacarrat</div><div class="ubbcode-body">My 25" WSM is hitting 3005FPS with the 180s. First barrel I got 3300 rounds out of the barrel before I installed the a 8.7 twist Rock. I was running moly at the time and it could have probably gone for the rebarrel a couple of hundred rounds earlier. So let's call it good for 3000 rounds. I highly doubt you will get anywhere close to 6k rounds out of the barrel with a SAUM. I would be shocked if a SAUM can even hit 4K rounds. I am sticking with the WSM. Remington brass isn't all that great, and even if you resized Nosler 300 brass, who knows how long it will last. My experience with Nosler stuff hasn't been all that great. </div></div>

What made you rebarrel?

What was the group sizes at the end of the barrel life?

 

[Bacarrat]

Re: Barrel length for the 7MMs? New build?

It was grouping around 9" at 300 yards. I tried a couple of different loads and made sure everything was tight. No go.

 

[mcfred]

Re: Barrel length for the 7MMs? New build?

On my new 7WSM build that's using a cheap remington take off bbl trimmed and rechambered to 25.5" I'm getting:

3000fps on 180gr SMKs with Retumbo (2900 with 68gr, mag primer)
3200fps on 162gr hornady matches with WXR
3400fps on 139gr hornady SPBTs with WXR

I've got 180 Berger, 175 SMK and a few more 162 Hrny matches loaded up but I haven't been able to get to the range lately to test them.

Going by the "Don Miller Stability Formula" calculator found here at JBM you should be alright with a 9:1 twist pushing 180gr at 2900+

My friend's 7WSM F-class gun's holding its group size even after 1300 heavy rounds though you can see the throat's losing its luster. I don't think you'll get 2x barrel life out of an RSAUM over a WSM, but if your goal is 2900fps with 180s and barrel life is a concern I too would go longer on the bbl and lighten the load.

 

[pmarauder]

Re: Barrel length for the 7MMs? New build?

The first thing to consider is if you are bound by your magazine length for your cartridge OAL? If so, that will effect your chamber freebore. If not, then i would go with a .160 to .188 freebore. This will put the 180 VLD boat tail/bearing surface junction right at your neck shoulder junction to maximize your case capacity in the SAUM My SAUM has a FB of only .101 because i am shooting the Berger 175xld which has the same BC as the 180 vld but a much shorter bearing surface. This allows me to achieve 3100 fps out of a 30" Broughton 5C barrel.

30" may be to long for your needs, but works good for me and the H-1000. you can get around your 2900 target Vel with the 180vlds using a 26-28" and pushing 60.5g of H4831sc. (work up to that load)
Let me know if you have any more questions on the SAUM, if done quite a bit of research for mine....and i could help you out if needed.
Derek

 

[bohem]

Re: Barrel length for the 7MMs? New build?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Team-Send-It!!!</div><div class="ubbcode-body">if you want 2900fps i would recommend a 28" that way you won't have to push it as hard to get there. 9 twist all the way, i prefer the palma contours over the rem but not a big deal.

I can damn near guarentee you won't get 2x barrel life of wsm it will be better and you do see more benchrest and f class guys use saum because it has longer neck shorter case=more efficient and easier on your throat.

<span style="font-weight: bold">I can't say to much though because i am about to build a 7/300 mag and i am hoping to push the 180's to 3100fps. </span></div></div>

Run Retumbo....

My 27" 7/300 WSM (not 7/300 WM) is throwing 180 Berger Hybrids at 3102fps avg with 73.5gr of Retumbo.

 

[Tangodown911]

Re: Barrel length for the 7MMs? New build?

Good info guys thanks for the help.

I'm glad the "hybrid" rounds came up. These are new to me also. Can someone shed some light on these also? Why are they called hybrids?

 

[pmarauder]

Re: Barrel length for the 7MMs? New build?

Im also shooting the Berger 180 Hybrid which has a blended ogive of both secant and tangent to obtain a very high BC .674. The theory is that they will not be as seating depth sensitive at the 180 VLD's and carry a little better BC. These bullets also have a shorter bearing surface than the 180 VLD, but longer than the 175 XLD. You thould be able to push the Hybrids faster out of a 26" barrel than you would be able to push the 180VLD's with the same powder charge.

Also, These bullets like to be jumped about .010 which also reduces pressure and some say that with the reduced pressure will extend your barrel life and limit throat erosion.... maybe
Derek

 

[Bacarrat]

Re: Barrel length for the 7MMs? New build?

7/300WSM uses the 300WSM case which has a longer neck. The 300WSM has a little less case capacity, but will shoot right there with a normal 7WSM, they use basically the same load information.

 

[RBros]

Re: Barrel length for the 7MMs? New build?

I have built a few 7WSM's that will run 3050-3075 with a 180 in a 26" barrel. Most of them run right at the 3000-3025fps mark using H4831SC. This is at an OAL that will fit in an Accurate mag or modified AI mag. In my experience, there is very little barrel life difference between the SAUM and the WSM.

 

[JCH]

Re: Barrel length for the 7MMs? New build?

My last 7WSM had a 24" barrel and ran 3050fps with the 162 amax and R17.

 

[Aubrey]

Re: Barrel length for the 7MMs? New build?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bacarrat</div><div class="ubbcode-body">7/300WSM uses the 300WSM case which has a longer neck...

</div></div>

This. Many want a neck length equal to or greater than the bullet diameter. The 7WSM neck is nominally .86xD, whereas the .270 & .300WSM necks are .97xD. I suspect that Winchester set the shoulder forward on the 7mm to prevent chambering and kabooms in the .270WSM (?). This would be similar to what Remington did with the .280 (to prevent chambering in the .270 Win, which was also on the 30-06 case).