Help - 17WSM accuracy degradation

[Sieg]

I bought a Savage Bmag HB .17WSM for sage rat hunting hoping I'd get a decent shooter. Once I got the rifle the bolt design is ridiculous and the mag design so-so. Once disassembled the action take-down surfaces are miniscule.... truly a sad piece of engineering IMO. The muzzle crown had burrs on it that would shred a paper towel.

The accuracy in the factory Tupperware stock with serrated muzzle were mediocre after testing with 20 and 25g Winchester and 20g American Eagle.

So after hours of work fitting it into a Boyd's Pro Varmint stock, lapping the crown, and then bedding with Devcon I've started accuracy testing again.

My typical barrel cleaning has been 1 dry patch, 1 wet patch using BoreTech Eliminator letting it sit 10 minutes, 1 dry patch, then 6 or so passes with nylon bore brush wetted with BoreTech, then dry patch which takes 10 plus patches to get a nearly clean patch.

First test experimenting with action torques. (All targets shot top left to right order with same lot of ammo)

The next outing (3/24/2019) at 100yds starting with a clean bore (excuse the errant .22mag holes)

I expected the high right first round flyer on a clean bore, the next 4 had me excited, the next two targets are WTF! I checked the action torque and the front had loosened, retorqued and the shot the next two targets..... WTF again. Cased the gun.

Disassembled and checked the bedding and mounting surfaces, thoroughly cleaned it again, torqued the action to 30ip front and rear.

Yesterday I test fired again at 50 yards (top 5 targets .477" dots):

I rechecked the action torque after the 3rd target opened up again and it was fine. Shot the next two targets for confirmation and cased it again.

Got home and cleaned the barrel after those 25 rounds and it was amazingly dirty. It didn't appear to be copper fouling on the patches, just black. So I decide to give it a thorough JB bore cleaner and bore bright treatment, about 30-40 passes with each product followed with solvent brush and dry patching then a patch with a little Kroil.

Any idea as to what's causing the accuracy to degrade in this manner?

Other than it's a budget Savage built on a Friday before a 3 day weekend and retooling of machining equipment.

 

[justin amateur]

I found barrel temperature to cause problems the hotter it got.
I'd shoot 5, then stop and let the barrel cool.
If I didn't I ended up with strays.
50 shots, 200 yards, Barrel block Bmag

 

[Sieg]

Ambient temps in all cases were 44-54*, guessing wind chill -2 to -6, rifle in the shade. Typically I load and shoot 5, probably 45 second spacing between rounds, get up from the bench and reload another 5 in no hurry and repeat. I hand checked the barrel temp after the last target and doubt it was triple digits.

How long are you letting your barrel cool?

Have you checked temps with an infared heat gun by chance?

Is that 15g the most accurate ammo you've shot?

 

[justin amateur]

No temp measurement.
Fingertip only.
Single shot loading, 5 in a row, 30 to 60 seconds between shots.
Let the rifle sit until no heat felt.
Repeat.


Results for other 17 wsm bottom half of linked page...

50 at 200

I think I've come up with a useful scenario...maybe. :rolleyes: 50 shots at 200 yards, rimfire, whatever setup makes you happy. 22lr, 17 hmr, 22wmr, 17hm2, 17wsm, all brands, all types. Full benchrest setup, bipod, bags or one-piece test rest, it doesn't matter. Grab a chunk of cardboard, about...

www.rimfirecentral.com

 

[Sieg]

The AE 20g and Win 15g appear to perform close considering wind conditions.

How often do you clean the barrel on the 17WSM and what's your procedure?

 

[justin amateur]

I treat the 17wsm as I do centerfire.
3000 fps copper plated bullets will leave copper residue in the bore.
Solvent intended to deal with copper, rod, nylon brush, patch, push through, repeat until clean.
As the barrel polished due to shooting, it's become easier to clean.
Less copper deposits.

 

[Sieg]

How many rounds do you have through your barrel?

 

[justin amateur]

The rifle has just over 1500 shots through it.

 

[ManoftheNortH]

The torque on your action screws make a world of difference if u have a Boyd’s stock because if u look at the stock without the action and barrel in it you can see where the barrel rests on two posts right in front of the mag well if u have it too tight they will hug them posts too tight and cause bad harmonics even if you’ve glass bedded it in my experience mine shoots good and I didn’t bed my Boyd’s stock i shoot half inch groups at 100 yds

 

[Nodak]

If I take it out of the stock for cleaning today, I'll get a picture but when I bedded mine into the Boyds stock I bedded the rear tang, trigger assembly, rear post, ront post and couple inches of barrel. I may have even did the sides. I'll just get a pic loaded up later today. I do remember it didn't come apart real easy and I almost left it glued together. If I remember correct I use something like 18 in/lbs.

 

[Nodak]

 

[Nodak]

And it was more like 40in/lbs. Solid as a rock. I re installed at 25in/lbs.

 

[ManoftheNortH]

Yeah you want it to be about 15 or so right before it starts to get actually tight this is the group I got 10 minutes ago today at 50 yards 5 shot group with one little flier due to my pull

 

[JG26_Irish]

I have had a Bmag for more than 6 years. Mine is the pencil bbl and they were notoriously poor accuracy. I broke mine in with careful 5 shots clean the bore, 5 more clean the bore for about 100 rds. A little polish with JB's. Then bedded it into a Boyds stock. I have a small rubber bumper at the front of the forearm pushing up slightly on the bbl. I clean it like a centerfire only more often and put more work into it since the tiny bore fouls quickly. When I clean mine it takes me about a week. Wet patches, bronze brush, more wet patches and then wait overnight more we patches and wait, repeat until no hint of copper fouling is coming out. I don't go crazy with the brush but these are always very fouled after a range session. They do not require re-seasoning like a 22lr. The first 15 shots will be the best and then who knows. Mine likes the 25g ammo better than the other lighter stuff. I recently got some of the 15g lead free stuff but have not tried it.

Heat will cause it to walk. I see variance after only 4 shots. It has a perfectly centered cold bore shot and will print three shot clovers at 100y on a calm day. I put a limbsaver rifle barrel stabilizer on it and that seems to have helped slightly but I have not had it out enough to make a strong recommendation yet. It is a good hunter, varmint getter, Not a good benchrest rifle. It is my #1 coyote getter but I don't often get shots over 200y on yotes. I can knock the center out of clay birds at that distance from a bench or solid prone rest. For what it is, it is a good rifle. The ammo is the limiting factor just as it is in the 17hmr and 17HM2.

Mine has ccnsistently grouped about 0.700" at 100yds and 1.300" at 200yds since new.

Posting three pics. #1 The rifle. #2 The black/white bull is 5 shots slow fire at 90yds. All in one hole except the last one where the bbl got hot. I think the white ring is 1" in this case and the group well under 1". #3 is three shots at 200y which measure under 1.5". The grid in the pic is 1" squares. I love it. I would call it a 3/4 moa shooter at practical distances if you shoot from a bench/solid rest and have NO WIND, and the bbl is clean. Otherwise you have all of the other Bmag shooters who treat it like a 22lr and wonder why it will not group after shooting 500rd at prairie dogs in a 10mph breeze.​

 

[ManoftheNortH]

Yeah I have the heavy barrel and it also likes the 25 grainers it also like 20 grain American eagles they sometimes even shoot better then the 25 grains I too have learned that I need to clean it after every 5-20 shots I didn’t break mine in bra cause I knew nothing about this but I now take very careful cleaning procedures I use special solvent made for cleaning copper and copper protection
I have been on the fence about bedding it as I have produced some fine groups as is I have also learned that they shoot well when the action screws are set to a low torque like 15 lbs or so here’s a group I shot yesterday with one flier due to my pull 75 yds it was the first shots out of a cold clean barrel I live my bmag I will also post a shot of it tell me how you guys like it or not I put a leupold cz freedom on it do any of you have different points of impact say if you sight your rifle in at thirty mine shoots high at 50 like 2 inches high any info on that???

 

[ManoftheNortH]

Correction leupold VX-freedom not cz freedom damn autocorrect leupold vx freedom 3-9x40