Recently purchased a Shilen DGA built 7-08. Almost every group (3 shots) has 2 touching and one out, 1/2 to 1". I suspect the bolt is hitting the barrel. Without removing barrel, what or how could I find out if this is the case? I also will switch scope, in case that is the problem. Thanks for any tips. Ron.
Bolt face touching barrel, maybe?
- Thread starter WyoWindage
- Start date
As a first very easy test you can take a sharpie pen and blacken the end of the bolt and put in the action and close the action and open it again. If the black is smeared there is definitely contact, if you do not see smearing it probably is not touching but no guarantees on that. Another way that sometimes makes the smearing easier to see you can draw line like spokes on a wheel as that will make the smearing easier to see than all black.
Maybe a better start is to know why you think the bolt is touching? After that is known the diagnosis might be easier, but the methods outlined above will cause no harm are pretty cheap and quick so probably little down side.
Maybe a better start is to know why you think the bolt is touching? After that is known the diagnosis might be easier, but the methods outlined above will cause no harm are pretty cheap and quick so probably little down side.
I have tried the ink, carnuba wax, and scotch tape about 20 times. I "think" it is smeared, even use a mag glass, but wonder if my pre-concieved ideas are playing with my eyes. It just throws those shots out with no reason. The scotch tape is scraped off, but maybe too thick for the thin gap, I don't know. I can't feel any foreward motion of the bolt after closing, pretty tight. It has such a nice barrel finish, I cringe to think it might be marred by removing it, but may be my last choice. Another option may be to file/stone the end of the bolt. It is a flat bolt head and the wear appears to be on one side, on the front of one lug. Would prussion blue help me any? If the gap is like .00l", would the bolt touch when fired even though it is not otherwise? I know this is a shot in the dark on my part, but I just feel that is what is going on. Thanks. Ron.
With one piece of scotch tape, it might close. With two it should not.
Pull the firing pin assy out of the bolt. Now place a dial indicator on the rear of the bolt. See if you can move the bolt fwd or aft. The gauge should read the clearance between the rear of the bbl and the face of the bolt.
Most smiths will cut that clearance at approx. .005". Some a bit more but would not exceed .010".
Bob
Pull the firing pin assy out of the bolt. Now place a dial indicator on the rear of the bolt. See if you can move the bolt fwd or aft. The gauge should read the clearance between the rear of the bbl and the face of the bolt.
Most smiths will cut that clearance at approx. .005". Some a bit more but would not exceed .010".
Bob
Try using a candle or oil lamp to smoke the bolt face. Any soot which is removed will be very easy to see. Also in a previous thread someone mentioned neck tension causing fliers. Just a thought.
Will remove firing pin and check play. Also the candle soot sounds interesting. Thanks to all for the tips. Will report back on my results. Ron.
you can check for bolt to barrel clearance by putting a dab of grease where you think it is rubing and cut a small sliver of lead from a bullet tip and put it on the grease. put in the bolt and close, open bolt remove the smashed peice of lead and measure . if it is not smashed you have at least that much clearance
Here are a couple 100yd targets showing the 2 in/1 out groupings (in general anyway). I removed the firing pin and played around with the bolt/barrel movement. Very little, maybe .001". Using black marker I could easily see the scrape when the bolt was fully moved foreward, but just a smidge when kept fully back in the receiver. I stoned a little more off the bolt, will see what happens next time out.
I'd flesh out whether that is a load issue before I did too much to the gun.
I had one batch of brass that was developing donuts at the neck/shoulder junction (on a minority of the cases) that started throwing groups that looked just like that. Donuts weren't severe, but enough to cause variation in effective neck tension.
I eventually fixed that problem by oversizing the necks, expanding them with an expandiron, then turning off the donuts. Eventually replaced that brass with a fresh batch of Norma 7-08 brass and all has been fine since then.
An easy test is to segregate the brass that shoots two together (mark them when you shoot them) into a batch and shoot those into a group.........that should tell you whether it's a brass issue.
Elkbane
I had one batch of brass that was developing donuts at the neck/shoulder junction (on a minority of the cases) that started throwing groups that looked just like that. Donuts weren't severe, but enough to cause variation in effective neck tension.
I eventually fixed that problem by oversizing the necks, expanding them with an expandiron, then turning off the donuts. Eventually replaced that brass with a fresh batch of Norma 7-08 brass and all has been fine since then.
An easy test is to segregate the brass that shoots two together (mark them when you shoot them) into a batch and shoot those into a group.........that should tell you whether it's a brass issue.
Elkbane
Tuesday session, five 3 shot grps. Wind from R to L-20-25mph. Five loads with Horn 162 VMax seated into lands. 37.0, 37.5, 38.0, 38.4 and 38.8gr IMR 4064. First groups show what wind did from a previous center impact, a good inch to the left. These groups indicate to me that the bolt/barrel touching problem has been solved, as only one unexplained vertical flyer (prob me or the load). The last two groups looked pretty good, .31 and .69 inch, with one to right prob slight wind letup.
I was concerned with neck thickness after my first outing. I used new Fed Gold Medal cases. They measured about 0.316" loaded. Chamber dimensions seem to show from 0.316 to 0.317". I formed some more cases and neck turned them, just cleaned up about half the case neck (These FC cases, about 10 yrs old, have the worse case wall variations I have ever seen!). Anyway they measure about 0.315" loaded. Still maybe too close?
Thanks again for all the help. Maybe I can get into some serious longer range shooting now. Am almost out of 4064 powder so may have to try something else. It's slim pickins around here.
Lapua40X
California Hunter Education Instructor
Re: Bolt face touching barrel, maybe? "PRUSSIAN BLUE"
Run down to your local auto parts store and pick up a tube of Prussian Blue. Smear a very thin film of it on the outermost edges of the bolt, close the bolt, open the bolt and check the breach (with a good pen light) and the face of the bolt. You'll know immediately if there's any contact between the two surfaces.
Run down to your local auto parts store and pick up a tube of Prussian Blue. Smear a very thin film of it on the outermost edges of the bolt, close the bolt, open the bolt and check the breach (with a good pen light) and the face of the bolt. You'll know immediately if there's any contact between the two surfaces.
Take some small rosin core solder and bolt grease. Put the grease on the face of the bolt cut the solder to match the face of the bolt and close the bolt. measure the thickness of the solder and it will tell you the distance the bolt is from the barrel. Most of the time you want about .0005 between your bolt and barrel. Do it a couple of three times to get a good measurement.
Erik Cortina
Team Lapua Brux Borden Captain
Supersparks said:
I'm sure you mean .005"?
Poor pic, but shows scraping with a red paint pen applied, firing pin in bolt, sized case, and trigger pulled. It didn't seem so bad in earlier tests, but I never pulled the trigger. Maybe that caused the extreme scraping I am seeing now. I tried some plasti guage, .001-.003", I think, but it just scraped off the bolt and got lost in the receiver. Guess I need to remove the barrel and remove some metal from it. Don't want to stone any more off the bolt head. Thanks again for all the help. Will report back with results when available. Ron.
Check to see how much play between bolt body and rear of receiver. Most of your touching appears on lower lug , which tells me , because of remingtons angled sear engagment , it pushes the rear of the bolt up into top of receiver . When this happens , it unloads the 6:00 lug . The more clearance between bolt body and receiver , the more it moves away from the bottom locking lug . Then when you pull the trig it unloads and moves , lowering the 6:00 lug closer to the receiver . Bill Calfee did the experments and articles in Precision shooting .
I would first check your bolt , to see if its True . Then , cock bolt on empty cartridge ,with finger on bach of bolt shroud , put pressure on bolt shroud and pull trig . Note how much it moves DOWN into rear tang .
Sorry for rambling , I ve not finished my coffee yet . Your rifle may have been assembled correctl y and with wear , now has bolt / barrel issues . When I say correctly , I mean it was not touching when assembled. Was probably a few,couple of thousands clearance , I usually use .005 as max .
I would first check your bolt , to see if its True . Then , cock bolt on empty cartridge ,with finger on bach of bolt shroud , put pressure on bolt shroud and pull trig . Note how much it moves DOWN into rear tang .
Sorry for rambling , I ve not finished my coffee yet . Your rifle may have been assembled correctl y and with wear , now has bolt / barrel issues . When I say correctly , I mean it was not touching when assembled. Was probably a few,couple of thousands clearance , I usually use .005 as max .
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.