I cut my choke off, how much velocity did I lose

 

It increased velocity slightly.

I recrowned the barrel, then polished the crown with #7 grinding compound and finished the polish with Flintz. Then tested for burs with a q-tip. The remaining 21 inches of barrel displayed extreme consistency when slugged.

All things being equal, in this case 25 bore, cuttuing the breech end off, in the past I have experienced a drop of around 15 fps per inch, in this case, cutting off the choke offset the velocity loss.

I was not experiencing clipping, however If you have ever experienced clipping while chronographing a string, you will notice that clipping reduces velocity, a choke can do the same thing to velocity, that speeding projectile hits the choke and slows down.

It is a dedicated slug shooter, making 85 FPE with mid 40 grain slugs sized .001 over groove diameter. While it is possible to get choked barrels to shoot well with slugs, I have one, but in the past decade of shooting slugs in airguns, I have had far better luck with unchoked barrels, so why mess with the choke. So if the twist rate is correct, in my opinion your always better off unchoked for slugs.



Regards,

Roachcreek

True, and a poorly executed crown is a death sentence to accuracy.



Roachcreek

I always found it easier to go .001 over. That and all sizing dies are not created equal, nor are measuring devices, or the condition of those devices. My first airgun mold I had made, I sent my groove diameter slug to Veral so we were on the same page. These days when I order a mold I specify it to drop .001 over with pure lead to cover all the bases. .001 has worked well for me out to 615 yards on 12 oz cola cans.

Always looking for that shoot as cast slugs, a task that is a lot easier with given the bump up you get with pbs.

Powder burners are different of course as are black powder cartridge rifles. As a caster of 50 years I had to relearn a lot when I got to airguns.

I remember around 10 years ago a ‘expert’ on the old Yellow forum told me I was wasting my time trying to get bulleted projectiles to work in airguns.



Roachcreek

I lube with 30 wt silicone oil, in zip lock bag, and shoot from the bag. I also use the oil to size with as my molds are either chosen or made to drop at a specific diameter, so sizing is minimal. The further you size a bullet down, the more risk you take in deforming that bullet.



Now read that last sentence again. Now imagine sizing for a choke by sending a undersized bullet, again sized for the choke at 920 fps to an abrupt choke. Now if you had a gradual taper to the barrel from breech to muzzle, there would be no impact in that last 1.5 to 2 inches. Which takes us back to sizing again, one way to alleviate potential damage is if your sizing in steps, say a .458 bullet you just think would be great in your .452 bore, size to .457 then to .454 and finally to .452, I used to do this in a Casull, but only going to .454 in that case, accuracy did suffer some, but I was after the neighborhood elk and they were close in and big. If I have to size in such a manner, I use Imperial Sizing Wax.



Many custom bullet makers size to .249, most groove diameters, such as LW are .254, the bullets chamber easily, but accuracy suffers. In that case a .249 or slightly smaller choke would be okay.

The good news is that some bullet makers do size to .254, and if you have a .252 bore, such as the Seneca 2500, not the Sumatra which is .254 I have been told.

Regards, 



Roachcreek