MarauderAirRifle.com

[Supercharged86]

I've never been able to find a advertised BC for the EJ 16.1 so I decided to finally conduct my own BC experiment using the fps vs. distance calculation. I tried this once before using a shorter distance but was never really convinced this was an accurate measurement, so I decided to try 50 yds instead. Now my usually muzzle (18" stand-off) velocity at 2650 psi is 900-910 so I was very curious what it would be at the 50 yd mark. After setting up my target and chrony I fired off 10 rounds, the chrony measured them between 774-761, fairly nice speeds given the distance, I think. Well according to Chairgun this gave me a BC of about .037, which seems to be at the high end of BC's. Now obviously the only way to get a more precise measurement using this calculation would be to have two chronys set up, measuring the given shot simultaneously. On a side note, I also managed a fairly decent grouping with just the one flyier. Cheers. Steve

[jlc]

Looks like you have that gun dialed in, nice velocity and great group, super shooting.


jlc

[Supercharged86]

Looks like you have that gun dialed in, nice velocity and great group, super shooting.


jlc

Thanks Jlc, shooting fairly well with these and the CPH's. Still looking to do a full Greg Davis tune soon. Steve

[sacshooter]

Wow, That is a great 10 shot group at 50 yards

Roger

[lamerabbit]

I actually did this with the two chronographs at 50 yards, back in 1995, 1996, and 1997, and the value I got was .035, however that was out of a Career shooting at 1000 plus FPS, and all my tests over the years have shown a drop in BC when pellets are shot at that high of a velocity. So your BC is probably correct, or at the very least so close it won't change your trajectory even an 1/8 of an inch at 5your 50 yard mark.

Back when I built my air rifle ballistics program, I tested over 90 different pellets at the time, using too many different rifles to count. The thing that made me crazy was you could shoot the same pellet out of two different guns and get two completely different BC values for the same pellet, right out of the same box. I always used 25 shot strings to get my ballistic coefficient value. Turns out this problem was caused by large differences in the actual twist rate in a given barrel, and the degree of choke in said barrel. Then you throw the huge differences in muzzle velocities the different guns shoot at and you spend a lot of time saying what the #@*&$??? Oh yes, least I forget the difference between a clean barrel and a dirty one; like shooting two different guns.........

Most of the BC values that you will find on the web came from my program, not all, but then there is a lot of bad info out there....... Problem is you can't copy write information; my loss, airgunners gain!

Jim

[DaveShooter]

Nice Shooting Steve. Nice looking group too. You passed your test now lets go hunt'in.

[Ben cook]

Very Very cool stuff
Been way to busy lately and wow way to hot out side , to many days in the 90's but getting ready for Squirrel, going to adjust Mrod to ling some 21Gr H & N
I will try to post results with Hammer , Spring and Port settings

[Supercharged86]

Hi Jim, Thanks for the great information and appreciate the confirmation. As a sidenote, the damn pellets, which are suppose to be 16.1 grains are mostly 15.5 and 15.6 grains. I finally got myself a scale and boy was I surprised to see the results. I only had two out of 100 that were the advertised weight with some being as low as 15.4 grns. Maybe that explains the occasional flyier???. Steve

[lamerabbit]

Hi Steve:

Now, for the bad news, you will find that with most pellets, of course the lighter pellets vary less... I have a shooting buddy in the UK who had a 60 foot pound Rapid 7 in 22 caliber, her was always buying the big Beeman Kodiaks, also sold under other names, he was always complaining to me that he never know what weight pellet he was going to get. Many weighted 19 grains, and they did not shoot worth a damn out of his Rapid, but the 21 grain shot tiny groups at both 50 and 65 yards. But every time he bought a new tin he did not know if he was going to have to throw it away!! That would make anyone nuts...

The occasional flyer, is probably caused by static or dynamic unbalance, (ballistics term), or just a fancy way of saying that the pellet is not balanced. This tends to occur more with the larger caliber pellets because of the amount of air space in and around the pellets. It happens to all pellets it is just a matter of degree.

What it really means that the pellet is unstable when it comes out of the barrel, it will tend to veer off tract due to this slight imbalance and the fact that the pellet is rotating as it travels toward the target. The rotation is, of course, caused by the rifling in the barrel. One might jump to the conclusion that a slower twist rate would be much better, but as with all rocket science it just isn’t that simple.

The Crosman Premier heavies run form as little as 10 grains up to almost 11 grains, with most falling in between 10.2 and 10.5, of course I have found some “peewees” that were less than 9 grains, not sure if it was a oversized 7.9 or a undersized 10.5. One of the guys at our club bought 4a case of 22 caliber Premiers for his Huntsman, and almost half the pellets in all 4 boxes were flat nosed pellets……..

However to answer your flier question, the most likely cause is oversized head on that particular pellet. The last case of 10.5 grain Premiers that I bought are all oversized, and they would not shoot in either of my rifles! I fixes the problem somewhat by sizing all of these with a Beeman sizing die.

It is very disconcerting when you shell out big bucks to have a custom rifle built, only to find out that the only lead you can get is garbage! I started shooting JSB’s out of my custom pcp, but the accuracy is still not up to what it was or should be, but a least I can keep them inside a ¾ kill zone at 40 yards when I do my part. Before I started sizing this batch, I was having trouble keeping them inside an inch at 40 yards! The old die twos and the die sixes would shoot near .2” at fifty yards out of this same gun, just as long as the wind was not blowing. One just can’t get real rifle like accuracy with stamped hollow lead pellets; least wise not with just any pellet or just any batch.

Well, that’s the bad news the good news is that I have heard that Crosman is now making their pellets cleaner and better that they have since Bob Holtz left them. It was Bob and his team that designed the Premier pellets, and changed the face of airgun shooting! Maybe Crosman has learned that cutting corners, makes for bad pellets and dissatisfied customers, who will buy another brand like JSB’s if they don’t fix the problem. We can only hope. Sorry to go on so much, but there are just no simple answers.

The best way to prevent fliers is to eye ball them, with a magnifying glass and set a side any that look damaged, or that have big die stamping marks or other type deformations.

Jim

[lamerabbit]

Hay Steve:

Have you tried the Rabbit Magnum pellets? I just noticed that Pyramyd Air has them. They are bullet shaped 177 caliber and weigh 15 grains. I will try and clock them when I get a chance. They should have a very high ballistic coefficient if you try them first let us know. If not, I will test them when it finally cools down here, which seems like it will never happen,at this point.........

Jim