85 RDF Twist Rate

[xswanted]

Another twist rate questions guys,

Has anyone tried the 85 .224 RDF in a 8 twist?

Thanks in advance!

 

[Ned Ludd]

You'll probably want to run the numbers here for your specific setup:

https://bergerbullets.com/twist-rate-calculator/

The G7 BC and OAL for the 85 RDF are: 0.245 and 1.135", respectively.

The answer is that an 8-twist might work [marginally] for you with the 85 RDF, but it will depend largely on factors such as barrel length/velocity, and the elevation + temperature where you plan to shoot most often. IMO - an 8-twist is too slow for the 85 RDF unless you're pushing them pretty fast. According to the Twist Rate Calculator, a minimum 7.75-twist is required at 1000 ft elevation and 75 degrees F. As the temp and/or elevation decrease, the minimum twist rate necessary will increase.

So the question really boils down to what is the absolute minimum twist rate necessary to keep the bullets from keyholing at the target versus the minimum twist rate required to achieve the full intrinsic BC of the bullet. In my experience, using a slightly slow twist rate and conditions that are predicted to give up 1 to 2% of the bullet's intrinsic BC (i.e. Sg >/= ~1.40) will usually work just fine. A twist rate and conditions that are predicted to give up more than about 4-5% of the bullet's intrinsic BC (i.e. Sg </= ~1.30) is not acceptable, even if the bullet doesn't keyhole at the target, which typically becomes a noticeable issue at an Sg of 1.0-1.1 (or below).

 

[DukeDuke]

I shot some out of my 1-8" ar15 in 223, not good.
Out of the 1-7" ar, they were stellar!!!

 

[karrarararararar]

There's a shooter up here (also a forum member) that says he had good luck with in then in his 8 twist. He used them with 4895 iirc

 

[McFred]

I did a basic run-up and got sub MOA with 85RDFs in .223 Rem in an 8 twist. However, I usually shoot 5000' elevation and up. Berger says on my cold days I'm "stable" at 1.5SG or better.

SAAMI .223 Remington chamber (Manson reamer)
24" 1:8 twist
85RDF Blems at lands, roughly 2.365" OAL
Projecitles average 1.130" OAL
Commecial "FC" brass, prepped cases average 92.73gr each.
Primer: CCI 400
Bolt action, not AR.
Hodgdon BL-C(2):
23.0gr - 2546 fps
23.3gr - 2609 fps
23.5gr - 2624 fps
23.7gr - 2617 fps
23.9gr - 2658 fps
24.1gr - 2705 fps
24.3gr - 2720 fps
24.5gr - 2726 fps
24.7gr - 2747 fps
24.9gr - 2799 fps

 

[xswanted]

Thanks guys,

I’ve ran this through the Berger stability calculator and it comes up at 1.45 I believe.

However I shoot the 80 grain Berger from the gun now, which also comes up as marginally stable and at 1000 yards it groups as good as I can make it.

I guess I will have to just give these a try and see if they are any better. I don’t think the BC again will really do much seeing as they will be going slower but it might be an option.

Thanks again!

 

[r bose]

I shot some out of my 1-8" ar15 in 223, not good.
Out of the 1-7" ar, they were stellar!!!

Same here. 7 TW service rifle 20" barrel AR shoots great out to 600 yards slow prone.

Duke Duke, what speed and powder did you use?

 

[DukeDuke]

2000MR at 2670fps 18" barrel

 

[markm87]

Are these 85 RDFs jump sensitive?? Just bought 500 and the Ogive compared to the Barnes Match Burner is obviously pointier and appears like the bullets my be a little jump finnicky.

 

[markm87]

Well I guess I'll find out tomorrow. I have some RDFs, Match Burners, and Factory Match Burner 85s to run and figger out.

 

[markm87]

Wow are these RDFs impressive. Will definitely work AR Mag length, which I was worried about.

I'm still working up a load with N135 so my velocities are still modest.

But we shot the RDFs against factory, hot Barnes Match burners which were over 2700 out of a Tikka 23.75 inch barrel. RDFs were just over 2600, but were about a Mil flatter at 1000 yards.

Still just getting started with the development/safe pressure, but looks really promising.

 

[Ned Ludd]

Wow are these RDFs impressive. Will definitely work AR Mag length, which I was worried about.

I'm still working up a load with N135 so my velocities are still modest.

But we shot the RDFs against factory, hot Barnes Match burners which were over 2700 out of a Tikka 23.75 inch barrel. RDFs were just over 2600, but were about a Mil flatter at 1000 yards.

Still just getting started with the development/safe pressure, but looks really promising.

Excellent! Glad you like them. I briefly tried the 85 RDFs, but didn't continue working with them as they weren't better than what I had already been using (90 VLDs, 88 ELDMs).

A note of caution with the RDF bullets - I had always wondered how Nosler obtained the almost needle-like points on their RDF bullets. I have more recently purhcased a few boxes of the lighter 70 gr RDFs, and a very large percentage of them have a pretty large bulge right near the middle of the bullet ogive/nose region below the meplat. It seems clear to me that the bulge was create by the [very] aggressive pointing method used. I did not a similar bulge in the 85 RDFs, so it may not be a problem with the heavier bullet. Nonetheless, it is something for which to be on the lookout.

 

[markm87]

Excellent! Glad you like them. I briefly tried the 85 RDFs, but didn't continue working with them as they weren't better than what I had already been using (90 VLDs, 88 ELDMs).

Have not shot the 90 VLD, but we shoot a lot of the 88 ELDMs. And as cool as the 85 RDF is... the 88 ELM is king.

The upside to the 85 RDF is that I can load them mag length and shoot them in ARs.