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Poor acuuracy - What's wrong?
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I am having accuracy trouble with my 7MM STW. It probably has 200-300 rounds through it as it hunting rifle and most of the rounds were load development or occasionally checking the sights. It’s my second rifle of this caliber and was 23 years old last summer. It has a Rem 700 action, a 1-in-11-inch twist Shilen barrel and a HS Precision fiberglass stock. My original load for it was a Nosler 140-grain Balistic Tip bullet over IMR 7828 powder at a little over 3,500 fps. Accuracy was generally about ¾ MOA or better. I used 8MM Rem cases sized to 7MM which were outside neck turned and nickel plated by a local metal plating company.

The original 3.5-10X Leupold scope worked fine for 400 yards or so but in 2006 (and for the next 8 years) Iowa had a rifle season for deer. I got a Leica rangefinder and had my .338-.378 Wea modified for long range shooting. Sometime in those years of rifle deer seasons I had the scope modified with Leupold’s “Custom Dial Reticle”. I mostly used the .338-.378 for long range deer but I did shoot a deer with the 7MM STW at nearly 600 yards and my grandson shot one at 540 yards with it. At those distances the 140-grain Balistic Tips made nickel size exit holes whereas the .338-.378 made 1-inch or larger exit holes at 700 yards. Anyway, I wanted a better long-range load so switched to Hornaday 162-grain ELD-X bullets at around 3,200 fps. A Hornaday rep said they would stabilize in the barrel with its 1-in-11-ich twist, even though the boxes the bullets come in say to use a 1-in-9.5-inch twist.

I developed the new 162-grain bullet load during the spring or summer but not when it was very warm. With that bullet and vary charges of IMR7828 (73, 74, 75, and 76 grains) I got a 4-shot group at 100 yards of less than 3/4 -inch. I selected a powder charge which gave about 3,200 fps. I like develop loads shooting groups with varying powder charges thinking it will better show powder/bullet combinations not sensitive to temperature/pressure variation. I have seen loads which are accurate in the summer but inaccurate in the winter. Using a fixed powder charge this load shot under a MOA at 200, 440 and 600 yards early in the fall but I did not have the gun perfectly sighted in with the new “Custom Dial”. I went to the range to get that done in October when the temperature was 12 deg F and got groups of at least several MOA not including bullets which missed the target paper entirely.

I figured the scope had shook lose and went back to the range in November with another Leupold scope on the gun and again got good groups. I did not write the temperature down as I usually do but am pretty sure it was warmer than 12 degrees. My assessment was that the previous scope had shook loose so I sent it to Leupold for repair but bought a new 3-15X Leupold scope with a “Custom Dial” reticle thinking the original scope might not be fixed soon. They sent the scope back saying that it “is” working properly but I don’t know that they meant that it “was” or if it was fixed. This morning I went to the range to sight it in with the new scope and it was 6 Deg F and again I got groups of several MOA at 200 yards with a couple bullets missing the paper.

I thought another potential problem was that I had added a silencer to it (before developing the 162-grain load) and had cleaned the silencer before shooting the bad groups in October. That is, the baffles would not have been oriented the same way as before. Then I shot a group at 100 yards with the silencer off the gun and also got a several MOA group. Now I am thinking that the bullets are not adequately stabilized at low temperature because of lower velocity and denser air. However, the holes in the target did not indicate key-holing and the groups were not just a little larger but many times larger. My next test will be to load up and shoot some of the original 140-grain loads to see if they still shoot OK. If so, I will probably assume the 162-grain bullets are not stabilized at low temperatures and try to develop a load with Hornaday 150-grain ELD-X bullets thinking a 1-in-11 twist might be OK for them.

Has anyone seen something like this where a rifle shoots good at regular temperature but “can’t hit the broad side of a barn” when it is cold? Or is there something else wrong with my rifle, scope or scope mount?
 
Posts: 257 | Registered: 25 November 2005Reply With QuoteReport This Post
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I would try another powder.
 
Posts: 3018 | Location: soda springs,id | Registered: 02 April 2008Reply With QuoteReport This Post
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Haven’t really seen that much difference because of the temperature variation, we’ve had excellent results with RL26 in a couple of different rifles, but they’re 9 twist and we’re shooting 168 and 180 grain Bergers.
 
Posts: 100 | Registered: 03 February 2009Reply With QuoteReport This Post
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I would try a bullet that is more suitable for a twist rate closer to what you have. Hornady reports shooting their loads with 1:10 twist barrel, and suggest a 1:8.5 for the 175 grain ELD-X bullet.

Sounds like you may be on the edge.



If ignorance is bliss; there are some blissful sonofaguns around here. We know who you are, so no reason to point yourselves out.
 
Posts: 2376 | Registered: 19 July 2002Reply With QuoteReport This Post
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1:11" twist is really slow for that long of a bullet. I'd ask a different Hornady Rep because there's no way that he should be recommending that bullet when the factory says it requires a 1:9.5". You might get a way with a 10" twist but I can't believe that an 11" twist would work.


Frank



"I don't know what there is about buffalo that frightens me so.....He looks like he hates you personally. He looks like you owe him money."
- Robert Ruark, Horn of the Hunter, 1953

NRA Life, SAF Life, CRPA Life, DRSS lite

 
Posts: 11770 | Location: Bakersfield CA. USA | Registered: 30 December 2002Reply With QuoteReport This Post
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I would look at the throat with a borescope. In my opinion STW's life is around 400 shots anyway. Maybe less maybe more depending on how hot the throat has gotten, but that will tell the story.

Of course you have checked every screw, bedding, crown, etc.

God Bless, Louis
 
Posts: 1244 | Location: Mountains of North Carolina | Registered: 14 January 2008Reply With QuoteReport This Post
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If you are using new brass for these loads, you may want to anneal the cases.



If ignorance is bliss; there are some blissful sonofaguns around here. We know who you are, so no reason to point yourselves out.
 
Posts: 2376 | Registered: 19 July 2002Reply With QuoteReport This Post
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quote:
Originally posted by youngoutdoors:
I would look at the throat with a borescope. In my opinion STW's life is around 400 shots anyway. Maybe less maybe more depending on how hot the throat has gotten, but that will tell the story.

Of course you have checked every screw, bedding, crown, etc.

God Bless, Louis


You could also use a Stoney Point (Hornady) tool to measure the OAL to the lands. I keep a log of all my rifles; one of my .300 RUMs that I measured recently didn't hit the lands at all; a borescope showed two are completely gone.


Don't Ever Book a Hunt with Jeff Blair
http://forums.accuratereloadin...821061151#2821061151

 
Posts: 7259 | Location: Arizona | Registered: 28 July 2004Reply With QuoteReport This Post
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Thanks for the comments. I just talked with a Hornaday representative and he said that the 1-in-11 twist of my barrel is far from what they would recommend. Also, I looked up stuff on air density and at 20 deg F with about any humidity the density is about 25 percent greater than air at 70 deg F at 60 percent humidity which is probably average for Iowa at mid-day. And bullets are less stable in denser air. I checked the throat recently and found that the 140-gr Nosler bullets touch the lands about 0.04-inch further down the barrel than they did when the barrel was new. At that point the accuracy had not noticeably changed. I think a new fast twist barrel would be a good solution but it’s not just the cost, there is also the time it takes to get a rifle re-barreled, and all the trouble, and the chance the next barrel might be a lemon. Anyway, I will check it again for accuracy with the old 140-gr loads and if that works out OK will try some of the Hornaday 150-gr ELD-X bullets and see what happens.
 
Posts: 257 | Registered: 25 November 2005Reply With QuoteReport This Post
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In the olden days someone came up with a "formula" that there was ≈0.005" throat erosion per 50-100 rounds in target rifles of .224/.30 cal as measured with an throat erosion gauge...going to the larger, hotter cartridges would increase that number considerably. Some of my hot 22/6mm/25 cal would do two to three times that number before accuracy started falling off and I would re-measure/re-seat out longer.

A 7mm STW is a LARGE cased, HI-VELO round...I wouldn't be surprised if it ate up 0.0001"-0.0005" of throat EACH ROUND. I've played with "Hot Rocks" for 50 odd years and I can tell you from first hand experience I've "worn" out barrel throats in 500 or so rounds...AND 7-8" of rifling to boot...a couple I never did get a good load before the barrel was wasted.

I't part and parcel of shooting Hi-energy cartridges and new barrels rather quickly comes with the territory.

A 1-11 twist will stabilize a bullet ≈1.25" long at 3200 fs in .284 cal...at 3000 fs that length drop's to ≈1.2". It's NOT the bullet weight that counts, it's the bullets LENGTH that is the limiting factor...twist rate formulas ask for CALIBER, VELOCITY AND LENGTH and if it is boat tailed.

Stick with bullets that are ≈1.2-1.25" long and keep the velo above 3200 fs and your accuracy will return...AND seat out closer to touching the lands...single load if you have to or accept the accuracy for magazine length cartridges.

Good Hunting tu2 beer
 
Posts: 1211 | Registered: 25 January 2014Reply With QuoteReport This Post
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I think some of the other posters hit the nail on the head.

Your load was probably "on the edge" in warmer temps but still shooting well. As temps got cold and 7828 was affected and velocities dropped off a bit, along with all the other things mentioned, the stabilization just isn't there with the 11 twist barrel.

When loads are on the edge but still shooting well at 100, they might go straight to hell at longer distances as the velocity falls off. As you know, this is one of the reasons we should all shoot at distance and so very many folks do not.

I think you're barking up the right tree by moving back down with your bullet weight (length).

Zeke
 
Posts: 1357 | Registered: 27 October 2011Reply With QuoteReport This Post
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quote:
In the olden days someone came up with a "formula" that there was ≈0.005" throat erosion per 50-100 rounds in target rifles of .224/.30 cal as measured with an throat erosion gauge...going to the larger, hotter cartridges would increase that number considerably. Some of my hot 22/6mm/25 cal would do two to three times that number before accuracy started falling off and I would re-measure/re-seat out longer.

That sounds like something I've heard from "BartB", (Bart Bobbitt).

He also had barrel life figured out to "pounds of powder" for various cartridges.

Bart is known for shooting a 20 round, 3.325" group at 800 yards.

https://search.aol.com/aol/sea...ards&s_it=loki-tb-sb


One shot , one kill
 
Posts: 197 | Location: North Carolina | Registered: 13 December 2002Reply With QuoteReport This Post
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Id prefer the gun in my lap to make any kind of suggestion..too much information.. Confused


Ray Atkinson
Atkinson Hunting Adventures
10 Ward Lane,
Filer, Idaho, 83328
208-731-4120

rayatkinsonhunting@gmail.com
 
Posts: 36276 | Location: Twin Falls, Idaho | Registered: 04 June 2000Reply With QuoteReport This Post
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With the specs you gave at 60 deg F (just an estimated temp I picked), that bullet at 3200 fps has an Sg (gyroscopic stability) of 1.291.

The minimum for accuracy is considered to be 1.3. Berger recommends when evaluating twist rates that you get to at or above 1.5 because below that you start compromise the BC of the bullet.

So at 1.291 you were just below/essentially at minimum which is why it probably shot "ok".

Drop to 12 deg F and your Sg is 1.172.

The above is likely your problem.


Mike



What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 100 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.
 
Posts: 9238 | Location: Loving retirement in Boise, ID | Registered: 16 December 2003Reply With QuoteReport This Post
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Just FYI, using the 150s and assuming 3250 fps Sg jumps to 1.405 at 12 degs and is 1.548 at 60 deg


Mike



What I have learned on AR, since 2001:
1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken.
2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps.
3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges.
4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down.
5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine.
6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle.
7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions.
8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA.
9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not.
10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact.
11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores.
12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 100 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence.
13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances.
 
Posts: 9238 | Location: Loving retirement in Boise, ID | Registered: 16 December 2003Reply With QuoteReport This Post
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