Effects of loose bore when shooting short bearing surface bullets?

[chop house]

i tend to shoot a lot of lighter for caliber (typically less bearing surface) and thin jacket, dead soft core bullets (ok, you caught me, i just described the speer tnt). They have shot quite well in a variety of rifles/calibers for me.

question is, would a bullet of that design have more accuracy problems in a barrel that has bore dimensions on the high side of 'acceptability'? does the thin jacket and soft core mitigate any of the negative effects of a slightly 'oversize' bore?

thanks

 

[243winxb]

Do jacketed bullets "bump up" (obturate) to fit the groove diameter? Is this the question?

I see accuracy problems and possible keyholing.

 

[chop house]

Do jacketed bullets "bump up" (obturate) to fit the groove diameter? Is this the question?

I see accuracy problems and possible keyholing.

i should have said "bore dimension" (singular) i was more referring to the bore diameter... what should be 0.237 (per saami) in a 6mm really at 0.238 (hypothetical number).

 

[243winxb]

I see accuracy problems and possible keyholing.

Oops bore and groove very different.

This may not apply then. The groove diameter makes the most difference, if oversize.
Had a factory M70 1965 vintage in 243 Win. Was told groove diameter was on the large side when trying to solve accuracy problems.

Took 10 fouling shots to get 85 gr Sierra hpbt's to shoot accuratly.

Tried sone 70 gr Rem match bullets. 3 shots hit the 100 yard target sideways. About 3" group. Ender up rebarreling it.

Only way to know, shoot them. Good luck.

 

[chop house]

Took 10 fouling shots to get 85 gr Sierra hpbt's to shoot accuratly.

Tried sone 70 gr Rem match bullets. 3 shots hit the 100 yard target sideways.

well, dang, i bet i gave too much discount on a custom rifle i sold a few years back, before i lucked up on this site..... and finally got some schooling:

i was having about the same issue... and tried lighter (shorter) bullets and cleaning the crap out of it. the mediocre to poor accuracy turned to keyholing just as you descrbed, and i gave up on it.

i should have mic'd a variety of bullets, tried the fattest ones with the longest bearing surface, slightly reduced the pressure, and left it fouled.

i like challenges but am in no hurry to repeat that experiment just for the sake of knowledge...

 

[BoydAllen]

FYI flat base bullets are going to slug up better than BTs. Within that style, a longer, heavier bullet with a higher proportion of full diameter shank may yield better results in the situation that you describe.

 

[Paw precision]

I think the tnt you described will yield .0026 of engraving so i dont see it being a problem as long as the twist rate is not way over and the speed is not above 3500 fps or so. Typically barrels for long range with faster twist are prescribing .0036 or so using .236 barrels and many are still utilizing the .237 for those as well whether the use is for varmint or match jackets.

 

[Dusty Stevens]

Softer they are the better they seal, but then you have that fragile jacket thing if you have a less than perfect barrel