7mm SAUM Rechamber/Barrel Life

[GSells]

Maybe we have come full circle in regards that , everyone switched from the 6.5 - .284 to the .284 because it was burning through barrels ? Now we are sort of back there again !?? Maybe ??

My 7/08 ai has about 1500 rounds on it and there is now no leading lands , but it still shoots really well , maybe the bestit Ever has . But Will it ever see 180’s at 2820 FPS ?? No! I’m using that same load to push the same 180’s at 2760 FPS . So I’ve had to compensate with more 2209 to keep it in a node !

I would rechamber it but if it still shoots really well , maybe leave it !?? It will maybe just let go one day and we can have a barrel burial ceremony!
But I’m trying to also like I think Peter , just use my fast ackley for 1000 , 900 yd work and use .284 800 and maybe 600 yds and try and spread the work load .

Unfortunately, I believe I’ll stuff a good barrel just trying to work out and prove the 280 ackley especially pushing 180’s at 3015 FPS ( although I can’t shoot that at Belmont , but I believe local ranges at 4100 ft pounds , so maybe at a prize meet here and there !)
But it does need to be put to the test to see if the ackley is as good as a saum ? I’ll either sink or swim! For that reason I’ve got a new Bart waiting to see if it is going to be a saum or an ackley!!
Umm be back from my gap year next year and we will find out , which I’m looking forward to!

But to answer the question, I agree with Brett B , and then again I maybe not qualified yet to say !
Regards Graham

[williada]

The 7 SAUM is a wonderful chambering and more efficient than a real barrel burner such as the 7 WSM. Its short powder column extends its efficiency to reduced loads which other chamberings may find difficulty achieving which group superbly and do take the pressure off the throat which hotter loads erode. This versatility allows you slip into another gear for prize meetings and long range should you wish with hotter loads to compensate for wind reading ability. Shot a lot of chamberings in my day and this one is my favourite. If I was to choose an all round rifle, the 7 SAUM has it all. Unfortunately in FO, money can buy a score and competitors will always be under pressure from SAUMS loaded up with fresh barrels.

[BRETT B]

Macguru , These figures of 900-1000 rounds are with 2209 which is very STOUT in the SAUM at 2950+ hence the reduced barrel life but the trade off is they are VERY Accurate and consistent.
You can however double the life with slower powders like 2217 but they can be a little tricky to keep tuned but some have had good success.

I have also found a SAUM soft loaded with 52-53 of 2209 at 2850 is a great accuracy load and basically gives you a 284 with better case and barrel life than at 2950.

I have played with many cartridges in F Open but I have to say that the 7 SAUM is now the pick of the bunch for me.

[RDavies]

Macguru , These figures of 900-1000 rounds are with 2209 which is very STOUT in the SAUM at 2950+ hence the reduced barrel life but the trade off is they are VERY Accurate and consistent.
You can however double the life with slower powders like 2217 but they can be a little tricky to keep tuned but some have had good success.

I have also found a SAUM soft loaded with 52-53 of 2209 at 2850 is a great accuracy load and basically gives you a 284 with better case and barrel life than at 2950.

I have played with many cartridges in F Open but I have to say that the 7 SAUM is now the pick of the bunch for me.

My thoughts exactly. 2209 is great for accuracy BUT it does seem a little hard on barrels when pushed hard.
I have heard of those using 2217 getting much longer barrel life, but I will stick with 2209. If I want to run at the 2830 FPS area, I still rather load the powder in a 284 case and get much better barrel life for slightly less ballistics

[GSells]

Brett and Dave I don’t disagree at all about the saum it’s proven and I have it really against me to prove the 280 ackley . I feel I have to some degree proved the lil 7-08 ai but only for short to mids .
Time will tell at a Queens near you soon , I’ll sink or swim ..... o rings and all !! Lol!

[Peterla]

My Hummer that I used in Ottawa has a round count of about 800. I have not shot it since we got back and I will be getting my Legend of a Gunsmith to take a look at it and let me know if its ready to rechambered to a 28 inch barrel.
I have 2 other SAUMs one with about 600 and another with about 200 so a bit more room to shoot. I now have a 284KMR for OPMs and club stuff to save the SAUMs for when it really counts.

[Longranger]

Although not a 7mm SAUM, I did an interesting comparison with 2 308 barrels at a 2000 round count. The barrels were one serial number apart, same profile, twist, finished length, crown and chamber. Both were loaded to the same velocity using the same cases and projectiles but with different powders. The barrel using 8208 showed more fire cracking than the other barrel which used 2206H. The barrel using 2206H did show considerably more throat erosion but less fire cracking. Figure that one out... Barrel care regimes were similar.

Although not a definative test, it seems to indicate that faster powder promoted more fire cracking but less actual throat erosion as seen with the borescope. My take on it is that slower powders seemed to have more of a sand blasting effect while the faster powder was hotter but for a shorter duration. The fire cracking was much more obvious with a faster powder. I guess you have to pick your poison.

I am not sure how that translates with a 7mm Saum but it was interesting nonetheless.

[BRETT B]

I have seen a similar effect with 2209 vs 2217 in the SAUM.
With 2209 i generally see firecracking start to appear about 1 inch past the throat/Lead , which is where the hard carbon starts to build up also hence the high heat of the 2209. Interesting is that the Lead tends to not move as much as you would think with such a hot powder and always looks better than 1 inch down the barrel after 900 rounds.
With 2217 the firecracking would appear a lot slower but it would be spread out over 6 inches starting 2 inches past the lead. it took many more rounds for the cracking to appear vs 2209 but once it was there it was a long way down and not much chance of a re chamber. this was at around the 1500 mark. I also noticed that with 2217 the land on the bottom of the bore at the start of the lead would end up being heavily scratched up after about 600 rounds. It took a bit of work to find out why but eventually the cause was from heavy powder residue left over settling in the bottom of the bore which the next fired bullet would have to go over.
Running 2217 at around the 2960 mark turned out to be too soft for the powder to burn 100% clean and needed to run well into the 3000 mark before there was no unburnt powder left over in the bore. Running the Saum at 3000 plus for me became a challenge to shoot consistently all day so after some solid advice from Rod and Matt I stuck with the 2209 and learned to adapt to its shortfalls of barrel life by being smarter with my tuning setup and make things repeatable .
1 year before Canada Matt P said to me " Use what works !! Not what you like!!" And to this day its the best bit of advice I have heard!!

[Peterla]

Hi Brett.
What was the challenge you felt with an over 3000 FPS SAUM? I just tested my Krieger SAUM with 2217 and found a nice node at 3025.
Your point on the other node at 2960 got my attention with the unburnt powder.
I also hade a really wide node at 2940 with 2217.
I will stew on that one.

[BRETT B]

Peter , @ 3000 plus and 62-63 odd grains of 2217 i found it harder to keep it grouping tight in terms of gun handling for a whole days shooting. Then trying to string 5 days together in a Queens I found the 2209 at 2920-2940 was just a lot easier to shoot and the gun tracked better so i stuck with what worked for me. Others may have better success as different style stocks may help with recoil and torque reduction.
The bar has been raised to such a high level now in F Open that making the rifle as easy and consistent to shoot as possible without fighting it all day is the only way I had a chance of keeping up with those Hot Shots from NSW

[Longranger]

I have found the same thing. Faster powders = less recoil and better tracking.

[John Smith]

Hi Marty, Phil and I have found 800 rds to be the mark for re chamber, however the second chamber gets shaky at 600rds,
Switching to Vlds seems to keep them going for another 200, and I will try some Lapua, to see if they have the same benefit,
No doubt the Saum is like a super model, high Maintanance
John

[DaveMc]

Marty - No doubt we have discussed this in the past but I will add to the group so everyone gets the input.

I had 2 barrels fall apart around 7-800 rounds after Raton and have looked down many with Borescope with PK - collectively maybe 20 odd barrels for rechambering . But to get a better picture we can go to the anecdotal evidence of UK and US.

In UK - where bisley is the norm and the barrel steel is allowed to cool between shots - 1200-1500 rounds seems common (talking to a few of the shooters from over there)
When discussing same with US shooters where string fire 20 shot matches (plus unlimited sighters in some matches) are the norm a couple of the high end shooters were rechambering as early as 400 rounds and 400-700 was typical according to them.

Here in Aus - so far it seems like 700-1200 is the mark depending on your shooting style. Rapid fire will shorten life dramatically.

[Pommy Chris]

Hope not a stupid question, but how about moly? 215's in a 308 need moly to keep pressures down so I really have no option. That said checking my med palma 215 barrel which shoots amazingly and it has 1800 rounds on it, wear is minimal and hardly any fire cracking, so plenty of life in it yet and load is hot ie 2700fps which is close to Belmont limit. Betta has a 185 barrel barrel she shoot naked bullets at 2820fps so really only a light load, same brand, same profile and checking it with a borescope it is stuffed after the same 1800 rounds. Only a small sample size of two barrels so far from statistically relevant, but interesting all the same. Wonder if moly may reduce chamber pressure in SAUM and give longer barrel life, just a thought? Re moly fouling in barrels it does not exist either, mine are spotless after a clean, worth mentioning. I do though paste every 500 or so rounds to keep carbon in check.
Chris

[John T]

Hello Marty.

2000 out of a 284WIN is a very good return. So is 1200 out of a 7RSAUM (54.5 of 2209?). But then, you've never been a "hot head". Unlike out two friends in the Field Artillery, Rod and Dave;
57.0 indeed !? No wonder your best is 800, Dave.

My limited experience has pre-taper-off (which can only be assessed with the hindsight of at least another 100 shots) for the WIN at about 1600 and for the SAUM at about 900; pretty much ball park.

Marty, I'm sure your trawling for information has nothing to do with economy and all to do with continuing the perfect life of THAT perfect barrel. If you believe that is possible (in my experience it is not) should not the first question be, has anyone extended unchanged accuracy to their hummer with a rechamber? I'm sure anyone who answers in the affirmative will answer all other questions.

If the urge to rechamber is irresistible, do it in one chop (like cutting off the dog's tail); 3/4" off the muzzle and 3 1/4" off the chamber; 30" to 26".

Here is an anecdote. Some years ago, Mark Buchanan told me of a conversation he had with Bert Bowden. Mark had won 3 or 4 Queen's with the same barrel which was well past 3000. He asked Bert if he should fit a new barrel. Bert said, " yes, after this one costs you a Queen's."

Regards,
John Tracey.
14.8.18
Never take doubt as your companion to the mound.