Bolt Locking Lugs and Accuracy
- Thread starter Mechdraw
- Start date
All of my rifles have had the bolt lugs lapped in as part of the normal barrel replacement process ; I really cannot comment on shooting a rifle that has not had this done. This would be an interesting test to grind off the face of a bolt lug and see accuracy differences. On occasion I have lapped bolt lugs in using valve grinding compound prior to final head space adjust and this is not a big deal to include in a re-barrel job but for an existing rifle more fitting would be required making things more involved.
Possibly you might coat the surfaces of your locking lugs with a felt tip pen, strip the bolt, apply force back onto the face of the bolt with a cleaning rod pushed down inside the barrel then work the bolt up and down. Hopefully both lugs will show signs of contact.
Possibly you might coat the surfaces of your locking lugs with a felt tip pen, strip the bolt, apply force back onto the face of the bolt with a cleaning rod pushed down inside the barrel then work the bolt up and down. Hopefully both lugs will show signs of contact.
Dusty Stevens
Shiner
You wont see it except your brass will expand crooked as the bolt face goes out of square and lift harder. Way more things to be concerned with first.
BoydAllen
Gold $$ Contributor
A good gunsmith can fix that for you, as part of blueprinting. He will set your action up so that it is running true to the CL of the headstock, and cut the front of the action and its lug seats so that they are perpendicular to the CL of the bolt raceway. There is other work that is usually done as well. The short answer to your question is that only having one lug make contact is generally accepted as being detrimental to accuracy. How accurate, and what do you use it for?
Hi BoydAllen,
Thanks for the reply. I shoot out 1000yds in F Class.
I can get 3 or 4 shots touching each other at 600 and 1 will be 1.5 minutes away, the next 3 or 4 similar and the next out by 1 to 1.5 minutes. With no adjustments.(wind was about .25 minute).
Quite often, this is a little bit deceiving and the root cause is not uneven seats in the receiver but a bore which is enough oversized at the bridge that the pressure of the sear against the cocking piece lifts the rear of the bolt up sufficiently that the upper (left) lug is out of contact with the locking lug seat. when the rifle is fired, the two lugs do make contact but threre is likely some variance as the bolt aligns itself under the pressure of firing.
In general, this sort of flaw results, not in a flier, but in vertical dispersion. Same thing if a lug is truly not contacting.
When the lugs are lapped, the rear of the bolt has to positively centered in the bore of the action. This can be accomplished with a sleeve (temporary or permanent) or with inserts which center the bolt when it's closed. Otherwise one can go through the "blueprinting" process and remachine the locking lugs and seats.
In the end, I'm not so sure the lug contact (or not) is causing your flier. I would expect to see a more general inaccuracy (comparatively speaking). One time that a single lug contacting has a real effect is when the ammunition is wet. WH
In general, this sort of flaw results, not in a flier, but in vertical dispersion. Same thing if a lug is truly not contacting.
When the lugs are lapped, the rear of the bolt has to positively centered in the bore of the action. This can be accomplished with a sleeve (temporary or permanent) or with inserts which center the bolt when it's closed. Otherwise one can go through the "blueprinting" process and remachine the locking lugs and seats.
In the end, I'm not so sure the lug contact (or not) is causing your flier. I would expect to see a more general inaccuracy (comparatively speaking). One time that a single lug contacting has a real effect is when the ammunition is wet. WH
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