Blowback

Question
Bob, is there a difference in the velocity of a semi-automatic and a bolt action rifle?A friend of mine said that a blowback system has less velocity than a semi-automatic.

Answer
Hi Ronie.

The action type itself does not determine the velocity of a given bullet. There are many other factors including the cartridge type, powder charge weight/type, bullet weight/type, primer type, barrel length, rifling type/condition, and numerous environmental factors. When you switch to a rifle with a different action type then several of these factors are changed so you can't make any direct comparisons.

If it were possible to keep all other factors the same and only change the action type then it would depend on the specific actions being tested. Some semi-automatic actions remain locked for the entire duration of the bullet traveling through the barrel and thus they can have performance similar to a manually operated bolt action. Some gas operated actions will bleed off excess gas to operate the mechanical parts and these could potentially result in less velocity with all other factors being equal however the gas operated actions are specifically tuned to accommodate this so you just can't make a blanket statement.

If you have a specific cartridge or rifle in mind then you can look up the ammunition specifications or reloading data for that cartridge to get a good idea of the variance involved. The only way to test specific rifle/cartridge combinations is with a chronometer at the range. You can buy a decent chronometer kit for only $80 and they are fun to test so you might split the cost with your friend and spend a few days at the range to answer all of your questions.

Hope this helps. Shoot straight and stay safe!

Bob