Allt har en början...

Idag så kommer ännu ett inlägg från John Bowkett, denna gång lite runt tillkomsten av nya R10..

R10 - The facts behind the factory change in barrel length.

There has been a lot of guesswork and illinformed  information put about on this subject.
The first production R10s were fitted with the same barrel as the Ultra which was 12” long and threaded ½” UNF. The regulator pressure settings for each calibre were determined using that length. Shot count was more than acceptable with the small 200cc buddy bottle fitted as standard and easily achieved the conservative figures used for marketing the product.

I chose the use of an Ultra barrel when I designed the R10 for a number of reasons. Sharing a component with another well respected model in the product range eases production. It  could also be fitted with a threaded bush instead of a moderator which functions in a way similar to the bull barrel S10 carbines. It centres the muzzle end of the barrel within the shroud and had grooves machined in its circumference allowing backflow into the breech end of the shroud helping silencing. Using a short 12” barrel also gave plenty of volume in the all important position for silencing which is ahead of the muzzle. The silencing properties of the shroud could be made even more effective by providing additional back pressure by using a short silencer of similar length to the original Ultra item before that was altered for marketing reasons.

Owners of new R10s found that when fitted with an additional silencer accuracy went to pot. The reason for this was the shroud material used was unsuitable. It varied in its inside diameter from batch to batch which didn’t help but the major problem was the fact that the bore was not concentric with the outer diameter. This meant that the threaded ends of the shroud were also eccentric to the rifling centre line. The front threaded shroud plug added to the problems.  Result, severe clipping, sometimes even without any additional silencer.  To solve the problem a source of decent, concentric bore with outer, aluminium shroud material was found and used. It didn’t stop there though.

To avoid any further problems with concentricity BSA came up with two bushes using O rings fitted internally and externally to centre the shroud on the barrel and the muzzle and breech end. Belt and braces as far as production was concerned. Belt and braces were thought to be not enough and so the barrel was increased in length to 15” which meant that a pellet has less distance to travel before it passed through the end cap of the shroud. This, given good concentricity of the shroud walls, should rule out accuracy problems and ease production. The downside of this for the shooter was the bush that centres the muzzle end of the barrel was altered in a way that prevented any backflow to aid silencing and the volume in front of the muzzle severely reduced by the decision to use a longer barrel with the same result.

The use of a longer barrel meant that the regulator pressure settings should have been lowered to suit and so aid consistency and remove the fear of any upward “spike” in velocity. They weren’t. On the plus side the longer barrel increased shot count.

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