I glass bedded my 378 Mk V doing the recoil lug first followed by the barrel lug. The final fit was nice and tight with clearance at the front, sides, and bottom of both lugs. After shooting about 10 rounds, however, the POI rose about 4" at 100 yards. Dropped after the barrel cooled, so something is expanding and pushing on the barrel. It occurred to me that as the barrel heats up it will try to push off on the barrel lug, which will tend to bend the barrel up. Anyone else experience anything like this? Any hints on how to bed the barrel lug? (or how not to bed it). Thanks.

I always bed recoil lugs with clearance below, in front and on both sides, so that the glass only contacts the rear of the lug. Don't have any experience with barrel-mounted lugs, though.

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Originally posted by sjmci:
After shooting about 10 rounds, however, the POI rose about 4" at 100 yards. Dropped after the barrel cooled, so something is expanding and pushing on the barrel. It occurred to me that as the barrel heats up it will try to push off on the barrel lug, which will tend to bend the barrel up. Anyone else experience anything like this? Any hints on how to bed the barrel lug? (or how not to bed it). Thanks.

This is common with all barrels. When barrels get hot they expand and move. If there is something interfering with their movement then groups suffer. The good news is that it returns when it cools.

If it were mine, and I didn't feel like physically removing the lug, and it shot good otherwise, then I would cut clearance around it and treat it as if it wasn't there. If the action is bedded well, then you shouldn't have to worry about not having a barrel mounted lug. Not on that caliber anyway.

I am having the exact same caliber/rifle being glassed and pilar bedded at my gunsmith right now, will let you know how it turns out. He has done several Mark V's for me that would wander and string shots vertical and has cured the problem. He also full length beds the barrel which stablizes the forend which seem to warp alot on Mark V's which puts uneven pressure on the barrel.

Hill Country Rifles, Inc. "accurizing" means pillar bedding along with the fiberglass. They re-barrelled and accurized the wife's .270 WeM Deluxe Mark V with stellar results.

Thanks to all who replied. SRT, pls let me know how it turns out. I find that interesting that he full length beds the barrel, I went in the other direction.