Hunting Washington Forum

Equipment & Gear => Guns and Ammo => Topic started by: Jeremiah P on June 11, 2009, 08:42:30 PM

Title: Measuring fps
Post by: Jeremiah P on June 11, 2009, 08:42:30 PM: Wondering the correct way to measure fps when trying out loads. It seems with a cold barrel the speed is slower than that of a warmed up barrel, after first shoot the fps range stays within 10 fps. Also what chronos are you guys using?
Title: Re: Measuring fps
Post by: Huntbear on June 11, 2009, 09:08:06 PM: Always shoot out of a cold barrel. That is how you hunt, right? I always wait at least 5-10 min. between shots, with the barrel pointed up slightly to help heat leave like a chimney.
I take a book or something to pass the time.

Chrony's do not vary much, but like all electronics, you get what you pay for.
Title: Re: Measuring fps
Post by: JoshT on June 12, 2009, 10:43:51 AM: Quote from: Huntbear on June 11, 2009, 09:08:06 PM
Chrony's do not vary much, but like all electronics, you get what you pay for.

I personally saw a test once where we took three of the exact same chronographs (Chrony Beta)... and set them up back to back so the round would go through all three right in a row. The velocities should have been very close... but there was as much as 100 fps difference between them. Sometimes the middle chrony was the fastest... sometimes the last one was the fastest. We rotated them around and got the same thing. My point is... there is no way to calibrate a chrony... and setting one up prefectly is nearly impossible.

Also, if the bullet does not travel through the lightscreens absolutely perpendicular to the screens and parallel to the bottom... then your readings will be eroneous. I use a Beta Chrony all the time... but I also take the results with a grain of salt. If you're looking for velocity to use for figuring a drop chart... you'll need to shoot the chart anyway... so an estimated velocity is a fine place to start.
Title: Re: Measuring fps
Post by: Antlershed on June 12, 2009, 11:14:11 AM: Josh, we are trying to get as close as we can to 3250 fps cause we ordered turrets based on a velocity and bc and the original bullets didn't shoot worth a damn so now we are trying to match it if we can.
Title: Re: Measuring fps
Post by: littlebuf on June 12, 2009, 02:30:01 PM: im not sure i understand, why are you trying to reach 3250 fps ?
Title: Re: Measuring fps
Post by: jeepasaurusrex on June 12, 2009, 02:53:51 PM: The BDC on the scope is calibrated for that load at that velocity.
Title: Re: Measuring fps
Post by: JackOfAllTrades on June 12, 2009, 03:12:03 PM: Shootin Chrony. Cold barrel.

I load for accuracy first, then velocity.

How close are you getting to that 3250fps? Think of it this way.. The BDC is calculated for that bullet weight/design at that velocity... Oh, but wait! What bullet and ballistic Coeficient? Round nose? Boat tail soft point? HP Spitzer? Each will have a different trajectory even if they were all fired at the same initial muzzle velocity. So, getting that magic number for fps isn't all that important unless you can duplicate exactly what the BDC is set for. If you can't duplicate it, then what you're looking to do is match the middle range impact point of the bullet to that same mid range aim point of the BDC. You might have to set the scope to have impact 1/2" high (or low), at that mid range to be able to use the BDC through its whole range.

The idea is to get you in the kill zone, not necessarily get you to the point of clover leaf groups at 100, 200, 400yds by using the BDC retical.

-Steve
Title: Re: Measuring fps
Post by: littlebuf on June 12, 2009, 03:31:53 PM: Quote from: jeepasaurusrex on June 12, 2009, 02:53:51 PM
The BDC on the scope is calibrated for that load at that velocity.

but what if that velocity shoots like crap out of that barrel? ive never worried about how fast my rounds are going just how accurate they are. i zero my scope accordingly and go with the best load. more than once its been the slower load
Title: Re: Measuring fps
Post by: Jamieb on June 12, 2009, 03:48:07 PM: antlershed.
What cartridge, what bullet?
Title: Re: Measuring fps
Post by: JoshT on June 12, 2009, 04:06:52 PM: They're shooting the .300 RUM... 180 Accubonds I believe.

Let me get this straight... you guys ordered BDC turrets based on unconfirmed drops? That's just asking for trouble... make sure you verify them before you go launching rounds at critters.
Title: Re: Measuring fps
Post by: Jamieb on June 12, 2009, 04:24:27 PM: I had a similar issue with my RUM/scope. I bought a shepard P-1A, I needed to get the 200 gr. accubond up to 3100fps to match the scope. 2 years of playing with loads and 1400 shots latter and I've got that load dialed in with the 200 gr accubond going 3175fps, it matches the cross hairs in the scope perfectly out to 1000meters. I'll never do that *censored* again. Plain old 1/4" or MOA turrets all the way.
Title: Re: Measuring fps
Post by: littlebuf on June 12, 2009, 04:51:42 PM: 1400 shots later!!! well now that you got your load you need a new barrel cuz that ones gotta be shot out
Title: Re: Measuring fps
Post by: JoshT on June 12, 2009, 05:12:11 PM: Quote from: littlebuf on June 12, 2009, 04:51:42 PM
1400 shots later!!! well now that you got your load you need a new barrel cuz that ones gotta be shot out

Hell no he don't... I'd hate to be a critter anywhere inside 1/2 a mile from that gun... that's for frickin' sure!
Title: Re: Measuring fps
Post by: AWS on June 12, 2009, 07:43:29 PM: Now all you need is a place to hunt that has wind flags all the way to a 1000yds.

AWS
Title: Re: Measuring fps
Post by: Jamieb on June 12, 2009, 07:44:01 PM: That remmy tube has almost 3000 rounds through it and its still shooting pretty good. I was out busting rocks at distances from 300 to 1100 yards a few days ago. I bought the rifle as a donor for a custom, made the mistake of shooting it.
Title: Re: Measuring fps
Post by: JoshT on June 12, 2009, 08:09:04 PM: Dude... never shoot the donor... you know that. :chuckle:

My 6mm also has a factory Remmy tube with over 3000 rounds through it... and most of those were 55's doing well over 4k... still going strong, funny how mileage can vary.
Title: Re: Measuring fps
Post by: Antlershed on June 12, 2009, 09:24:01 PM: In short, yes we were dumb and ordered turrets because we thought the bullets would shoot. We were wrong so now we are trying to work up a load to salvage the use of the turrets. We will be sure to test it all the way out and if the load isn't accurate or if the turrets don't work with it we will scrap the turrets and eat the money we spent on them. We are both shooting RUM's and 180 Accubonds. We are getting pretty close to 3250 with about 96 I grains of powder.
Title: Re: Measuring fps
Post by: JoshT on June 12, 2009, 10:26:30 PM: There's a bunch of different bullets that should work with that turret. 180 Swift Scirrocos, 180 Ballistic Tips, 180 Sierra SBTs, 190 Bergers, etc. I can't imagine the 180 Accubond not shooting well enough for you. Like I told both you guys... my Sendero 300 RUM only shoots MOA at 100... but it will hold MOA (and often better) for a loooong ways, and 8" groups at 800 yards will still hammer a coyote.

How "inaccurate" are your 180 loads?
What powders are you guys shooting?
Have you fooled around with the OAL?
Have you tried Moly (I know Jamie is a fan of the Moly coated 200 Accubonds in his RUM)?
Title: Re: Measuring fps
Post by: Jamieb on June 13, 2009, 12:17:14 AM: I'm not running moly in the RUM. One of the few rifles that still shoots naked bullets. I tried 180gr. partitions when I first got my RUM, they wouldnt shoot for crap. As Josh touched on, your 100 yard groups my not be showing the true potential of the load. My 300 RUM with 200 gr. accubonds is shooting 1 moa at 100 yards but consistently shoots 1/2 moa at 500 yards. The last time I was up in the hills shooting, the weather was perfect in the morning. I shot some unbelievable groups.
Title: Re: Measuring fps
Post by: Antlershed on June 13, 2009, 10:14:20 AM: Sorry, I should have stated that the 180 Accubonds are shooting great groups at 100 (holes touching). We are just trying to dial the speed in as close to 3250 as we can now.
Title: Re: Measuring fps
Post by: JoshT on June 13, 2009, 10:24:36 AM: I did some calculations for you guys with my ballistics program... and there's about 15 bullets that will work within half-minute of your turrets. In fact, if you shoot the 200 Accubond at 3100 (which is pretty easy) and sight your rifle in 1/2" higher than you would have with the 180... then the turret will be pretty much dead on all the way to 1000 yards (which is as far as my program goes).
Title: Re: Measuring fps
Post by: Antlershed on June 13, 2009, 10:36:20 AM: Thanks for the info Josh. My turret goes out to 1k and Jeremiah's goes out to 1200 (mine was supposed to).