I stopped by a friend's house today and he shot in his gun in yesterday with a new scopebut he said he had a problem with all the primers he used except 2 cracked, split and generally were blown apart. He was using 777 pellets, 250g pellets. I said this is usually caused by back pressure and you should lessen the charge. Since he is shooting sabots, he can't drop the charge 20g. Could there be any other causes of this? He only sighted in a 50 yards, and we getting a good 1/2 group, I don't think the split primers is normal, so wanted to ask the forum what they thought. I don't know what kind of primers he was using since he didn't have the package they came in. His gun is a Knight Disc (origonal not the newer red Knight Discs).
Chap Gleason

gleason.chapman

Think I might look at the breech plug... is the flash hole eaten out?

I am not sure what you are saying with "split primers" is the actual primer coming out of the battery cup?

My Remington's do this once in awhile - but not enough to re-cock the bolt...

I didn't actually see one, but that is how my friend described them to me.
The primer were literally blown apart. Yes, the flash hole could be an issue, I will call him and ask him to take a look at it. Chap

Check the 209 primer flash hole .... normally the sides are being eaten away and what is happening is blow back is hitting part of the primer and blowing it apart. I have that happening in my Knight Disc as well. But with the Disc it is not so bad because the primer holder for the most part keeps it in place.

The flash hole could be either too large OR too small and cause those symptoms. Doesn't happen to have a domed breech plug does he?

He is swabbing the bore after each shot isn't he? I would think he is given his reported groups - but you know how that goes. Some T7 crud buildup can cause excessive pressure - this I experienced first hand right after the powder became available. I was shooting loose powder though.

UC, Thanks. No, he is not swabbing. I asked him to buy another spare breech plug and check the diameter of the hole. I also talked to him about swabing, saying that the crud ring at the last inch or two is giving the bullet a lot more resistence to get started causing the blow back, he said he puts a patch of bore butter down about the 5th shot, cause he can't load a bullet. So I think he has to go for swabbing to rid himself of this problem or shoot the .25ACP small primers. Chap Gleason

I would probably advise him to leave the bore butter at home and use patches lightly dampened with Windex w/vinegar or similar for a swabbing agent followed by a dry patch.

Right. I will tell him that. Thanks Chap