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Posted: 3/10/2026 9:12:59 AM EDT
[Last Edit: VASCAR2][Edited]
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I’ve been curious about the temperature affects on velocity in the 6.5 Grendel. I have seen test on powder velocity variations at different temperatures in 7.62x51 and 5.56x45. The 6.5 Grendel in a semi auto is SAAMI limited to 52.000 psi plus it has a short fat case with a larger bore compared to 5.56. I recently purchased an Athlon Rangecraft RADAR Chronograph and decided to collect some data on my reloads at different temperatures. I can shoot on my property next to my residence but I didn’t shoot any groups for accuracy. I was just interested in capturing the velocity at different temperatures. The ammunition was stored outside from the previous day and I used environmental data from the National weather service at an airport approximately four miles from my residence. I also used my thermometers to try and get accurate ambient temperatures. I tested five different powders in the 6.5 Grendel and listed below are the specifics of each load. The ammunition tested was previously loaded from my current stock pile of powders, bullets, primers and brass. I decided to only shoot five round strings to limit the cost of this project. 1. Hodgdon CFE223, 31.0 grains, 123 grain Nosler CC, CCI450, Hornady brass. 2. Shooters World Match Rifle, 31.0 grains, 123 grain SST, CCI450, New Hornady brass. 3. Western Accurate 2520, 29.5 grains, 123 grain SST, CCI450, New Hornady brass. 4. Alliant AR Comp, 26.7 grains (max charge), 120 grain Nosler BT, New Hornady brass. 5. IMR IMR8208XBR, 26.8 grains, 107 grain Sierra Match King, Hornady brass. Powder at Temperature CFE223 Avg. 8* 2373.9 18* 2388.3 28* 2389.4 38* 2401.5 48* 2425.2 58* 2430.1 68* 2428.0 78* 2433.6 88* 2449.8 93* 2458.4 98* 2448.7 Shooters World Match Rifle Avg. 8* 2407.1 18* 2470.0 28* 2450.8 38* 2480.1 48* 2476.5 58* 2488.8 68* 2524.8 78* 2542.7 88* 2526.9 93* 2544.8 98* 2551.7 A2520 Avg. 8* 2289.4 18* 2302.2 28* 2310.0 38* 2335.6 48* 2354.6 58* 2376.5 68* 2372.4 78* 2410.2 88* 2371.5 93* 2393.1 98* 2388.8 AR Comp Avg. 8* 2342.8 18* 2335.2 28* 2344.4 38* 2345.1 48* 2370.0 58* 2337.7 68* 2333.0 78* 2330.1 88* 2324.9 93* 2319.1 98* 2324.0 IMR8208XBR Avg. 8* 2314.8 18* 2318.4 28* 2344.4 38* 2372.1 48* 2377.7 58* 2364.8 68* 2366.4 78* 2407.5 88* 2388.8 93* 2391.3 98* 2378.8 |
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The test rifle was an AR-15 I assembled using a Faxon (group buy) Monster logo 18” 6.5 Grendel pictured below. I live in the midwest and all shooting was done at 450’ above sea level at the same location. I did this test to satisfy my own curiosity and decided to share the results. I will attempt to capture more velocities at higher temperatures through the summer and will post my results. Here is a picture of the test rifle. 
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Here is more data captured during each test at the different temperatures. At 8* I encountered two stove pipe jams with Accurate 2520. It appeared this load produced insufficient gas at this temperature compared to the other loads. I did not clean or lube the rifle prior to this test. I did fail to capture the first round of CFE223 on the 8* test and only left five cartridges of each load in the cold prior to the test. In the future I left seven or more cartridges outside to get ammunition to the ambient temperature. On March 9, 2026 I encountered a failure to extract stove pipe jam with the second shot of CFE223. I cleared the jam and the next two cartridges jammed. I pulled the bcg and observed the extractor had broken. I replaced the extractor and continued the test. I had noticed the extractor was leaving fang marks on the case rims but I assumed the extractor would wear in. I was wrong but the new extractor was not leaving any marks on the brass. I thought this test would give me a basis of information in case I wanted to conduct a more thorough powder test in the future. Below is more additional data collected at each temperature. Powder Sensitive dates/Temp 12-14-2025 8:40 AM 8* CFE223 Avg., 2373.9, SD 15.8, ES 38.4, min 2350.1, max 2388.5 SW Match R., Avg. 2407.1, SD 13.5, ES 38.4, min 2383.5, max 2421.9 A2520 Avg, 2289.4, SD 8.2, ES 20.0, min 2278.5, max 2298.6 AR Comp Avg., 2342.8, SD 13.7, ES 36.4, min 2320.2, max 2356.6 IMR8208XBR Avg. 2314.8, SD 14.1, ES 40.4, min 2296.9, max 2337.3 01-18-2026 9:10 AM 18* CFE223 Avg 2388.3, SD 28.0, ES 69.6, min 2348.4, max 2418.0 SW Match R, Avg. 2470.0, SD 12.3 ES 34.4, min 2448.2, max 2482.2 A2520 Avg. 2302.2, SD 4.6, ES 11.8, min 2295.3, max 2307.1 AR Comp, Avg. 2335.2, SD 12.2, ES 32.8, min 2316.9, max 2349.7 IMR8208XBR, Avg. 2318.4, SD35.0, ES 107.3, min 2270.0, max 2377.3 01-18-2026 2:28 PM 28* CFE223 Avg. 2389.4, SD 30.3, ES 89.6, min 2355.0, max 2444.6 SW Match R, Avg. 2450.8, SD 12.4, ES 34.1, min 2440.3, max 2474.4 A2520. Avg. 2310.0, SD 5.3, ES 15.1, min 2302.8, max 2317,9 AR Comp Avg. 2344.4, SD 12, ES 34.1, min 2320.9, max 2355.0 IMR8208XBR Avg. 2344.4, SD 9.5, ES 23.3, min 2335.4, max 2358.9 01-22-2026 1:05 PM 38* CFE223 Avg. 2401.5, SD 19.7, ES 59.7, min 2368.4, max 2428.1 SW Match R, Avg. 2480.1, SD 13.2, ES 30.8, min 2464.2, max 2495.1 A2520, Avg. 2335.6, SD 8.1, ES 21.7, min 2325.8, max 2347.4 AR Comp, Avg. 2345.1, SD 10.0, ES 26.2, min 2331.0, max 2357.3 IMR8208XBR, Avg. 2372.1, SD 24.0, ES 72.8, min 2339.9, max 2412.7 12-17-2025 10:02 AM 48* CFE223 Avg., 2425.2, SD 5.6, ES 15.7, min 2417.7, max 2433.4 SW Match R, Avg., 2476.5, SD 15.5, ES 41.0, min 2459.3, max 2500.3 A2520, Avg.2354.6, SD 8.6, ES 23.0, min 2342.5, max 2365.5 AR Comp Avg., 2370.0, SD 13.7, ES 37.7, min 2309.4, max 2347.1 IMR8208XBR Avg., 2377.7, SD 42.3, ES 124.0, min 2322.5, max 2446.5 12-17-2025 12:23 PM 58* CFE223 Avg., 2430.1, SD 13.3, ES 37.7, min 2409.1, max 2446.9 SW Match R, Avg. 2488.8, SD 10.3, ES 31.8, min 2473.8, max 2505.6 A2520 Avg. 2367.5, SD 15.4, ES 41.7, min 2341.9, max 2383.5 AR Comp, Avg. 2333.7, SD 6.1, ES 17.4, min 2321.9, max 2339.2 IMR8208XBR Avg. 2364.8, SD 34.6, ES 104.0, min 2304.8, max 2404.8 03-09-2026 1:10 PM 68* CFE223 Avg. 2482.0, SD 11.2, ES 32.2, min 2407.8, max 2440.0 SW Match R, Avg. 2524.8, SD 11.1, ES 28.2, min 2513.1, max 2541.3 A2520, Avg. 2372.4, SD 14.6, ES 40.7, min 2348.4, max 2389.1 AR Comp, Avg. 2333.0, SD 10.8, ES 31.2, min 2317.9, max 2349.1 IMR8208XBR, Avg. 2366.4, SD 21.4, ES 58.1, min 2336.3, max 2394.4 03-06-2026 12:07 PM, 78* CFE223, Avg. 2433, SD 52.5, ES 137.8, min 2330.4, max 2468.2 SW Match R, Avg. 2542.7, SD 14.1, ES 40.7, min 2529.2, max 2569.9 A2520, Avg. 2410.2, SD 17.1, ES 48.9, min 2377.0, max 2425.9 AR Comp, Avg. 2330.1, SD 8.9, ES 24.9, min 2314.3, max 2339.2 IMR8208XBR, Avg. 2407.5, SD 22.0, ES 57.7, min 2376.3, max2434.1 06-06-2026 1:04 PM 88*. Ammunition kept out of direct sun light. CFE223, Avg. 2449.8, SD 34.1, ES 104.7, min 2387.1, max 2492.8 SW Match R, Avg. 2526.9, SD 5.9, ES 16.4, min 2518.7, max 2536.1 A2520, Avg. 2371.5, SD 6.2, ES 15.7, min 2363.2, max 2378.9 AR Comp, Avg. 2324.9, SD 10.5, ES 28.2, min 2304.8, max 2333.0 IMR8208XBR, Avg. 2388.8, SD 10.8, ES 30.2, min 2372.4, max 2402.6 08-15-2026 2:29 PM 93* ammunition kept out of direct sun CFE223, Avg. 2458.4, SD 27.6, ES 78.4, min 2410.8, max 2489.2 SW Match R, Avg. 2544.8, SD 15.3, ES 42.0, min 2521.0, 2563.0 A2520, Avg. 2393.1, SD 10.9, ES 29.2, min 2378.0, max 2407.3 AR Comp, Avg. 2319.1, SD 10.8 ES 29.9, min 2300.9, max 2330.7 IMR8208XBR, Avg. 2391.3, SD 19.2, ES 58.7, min 2363.8, max 2422.6 08-31-2026, 1:55 PM 98* ammunition kept out of direct sunlight CFE223, Avg. 2448.7, SD, 9.5 ES 26.6, min 2431.1, max 2457.7 SW Match R, Avg. 2551.7, SD 5.6, ES 15.4, min 2544.3, max 2559.7 A2520, Avg. 2388.8, SD 8.1, ES 23.3, min 2373.7, max 2397.0 AR Comp, Avg. 2324.0, SD 10.9, ES 28.2, min 2311.4, max 2339.6 IMR8208XBR, Avg. 2378.8, SD 12.8, ES 37.4, min 2355.6, max 2393.0 |
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I know but CFE223, LeveRevolution, Accurate 2520 and Shooters World ball powders produce some of the highest velocity in the 6.5 Grendel. CFE223 with 31.0 grains of powder with 123 grain bullets has been my go to load since getting into the 6.5 Grendel. I was curious how the velocities of ball powders would compare velocity wise to the more temperature stable powders like AR Comp, IMR8208XBR, StaBall Match and H4895 in colder temperatures. The weather didn’t cooperate in getting any lower temperature velocities. My area experienced some temperatures close to zero but my shooting area was covered with snow drifts from recent snows. Honestly as I get older (retired old guy) I’m not as likely to be out and about in sub zero weather. |
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Here is a link on the 7.62/308 powder sensitivity test on 6.5 BR/Accurate Shooter.com which is pretty good. https://forum.accurateshooter.com/threads/temperature-sensitivity-of-11-powders-for-308-winchester.4069771/ Here is some info I found years ago I saved. HS-6 1.21fps per * H110/W296 1.24 fps per * Imr4227 1.17fps per * Lil' Gun 1.31 fps per * RL10x .71 fps per* Benchmark .44 fps per * Imr3031 .73 fps per * Imr8208xbr .59 fps per * H4895 .23 fps per * Alliant Varmint pro .89 fps per * Alliant AR comp .77 fps per * Varget .19 fps per * W748 1.32 fps per * Imr4064 .53 fps per * Ramshot Tac .91 fps per * Imr4895 .87 fps per * AA4064 1.11 fps per * AA2520 .98 fps per * RL15 1.52 fps per * from 50* and up PP2000MR .99 fps per * Imr4320 1.32 fps per * Ramshot Biggame .98 fps per * H380 1.44 fps per * VV N150 1.08 fps per * H414/W760 1.42 fps per * Imr4350 .64 fps per * AA4350 .47 fps per * H4350 .29 fps per * RL17 1.42 fps per * Hybrid 100v .78 fps per * RL19 1.61 fps per * VV N160 1.24 fps per * Imr4831 1.19 fps per * Ramshot Hunter .86 fps per * H4831 .36 fps per * RL22 1.71 fps per * Imr7828 1.36 fps per * Magpro 1.01 fps per * H1000 .21 fps per * RL25 1.59 fps per * Ramshot Magnum .87 fps per * Retumbo .49 fps per * RL33, still trying to get my data for this one. US869 1.68 fps per * H50bmg 1.64 fps per * |
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Originally Posted By pomofo: Thanks for the very interesting information. It's a little concerning to me because 2520 is my go-to in both Grendel and 5.56 right now. Do you happen to have links to the temperature data you mentioned on 5.56 and 7.62x51? Western and Hodgdon reloading data show 29.6 grains as a maximum charge for Accurate 2520 where I used 29.5 grains. My sample size of five cartridges at each ten degrees of temperature change isn’t a large enough sample size to give very precise data. I do think my results do show the general trend on how temperature affects velocity especially for ball powders. My results from A2520 show pretty small extreme spreads. As I collect data at higher temperatures I hope to do some accuracy testing. My load of 31.0 grains of CFE223 is less than Hodgdon maximum charge of 31.2. Shooters World and Hodgdon data is for 123 grain SMK. The Shooters World Match rifle data shows the max charge of 31.4 grains. I chose to use 31.0 grains of SW Match Rifle since I was using 31.0 grains of CFE223 and they are of similar burn rate. |
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I've been using the old Alexander Arms reloading data, so I load my 123 Scenars with 30.5 grains of 2520, which is 0.2 under max. I got 2561fps from a 16" barrel indoors, I would imagine that would be a lot higher outdoors during the summer. Which brings up another question since I've read a lot of speculation about how the formulation of 2520 has changed over the years and the burn rate has fluctuated. I'm still working off an 8-lb jug from 2007, when was your powder produced? |
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If you go from 38° to 78° , thats pretty much the extreme spread im going to shoot in . 48° to 88° would probably be a more accurate reflection of my shooting environment. Not a big swing in velocity/pressure in that sample . Good work youre doing here . Thanks . |
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Originally Posted By pomofo: I've been using the old Alexander Arms reloading data, so I load my 123 Scenars with 30.5 grains of 2520, which is 0.2 under max. I got 2561fps from a 16" barrel indoors, I would imagine that would be a lot higher outdoors during the summer. Which brings up another question since I've read a lot of speculation about how the formulation of 2520 has changed over the years and the burn rate has fluctuated. I'm still working off an 8-lb jug from 2007, when was your powder produced? My Accurate 2520 was purchased in the last five years and is all manfactured at the same facility. I have some older Accurate #2 which was manufactured in Canada and newer Accurate #2 which was manufactured in the US. The color of the powder was different and I noticed a change in volume using my Uniflow powder dispenser. A Friend reduced his powder charge of A2520 after the location of manufacture changed. I always thought AA 6.5 Grendel data was pretty hot for some powders. I still have the Alexander Arms reloading data saved. I load all my ammo with a RCBS Rock Chucker, 10-10 balance beam scale and RCBS Uniflow powder dispenser. I bought my reloading gear back in the early 80’s and it works. I contemplated using loads with different powder and bullets but I thought these five would be a good place to start. The IMR8208XBR load is a light target and plinking load with factory seconds bullets. I was most curious about AR Comp as I read it was very stable until you got below 0* F and velocities would then increase. The Athlon Chronograph only failed to capture one shot because I was to far from the Chronograph. I put the Chronograph on a tripod at shoulder height and shoot off hand next to the Chronograph. Very easy to set up and use. |
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I have posted the actual velocities of each shot on each day with environmental data on the 6.5 Grendel forum. There is less traffic on that forum than ARF.com if anyone wants to check it at the link below. https://www.65grendel.com/forum/forum/-6-5-grendel-discussion-forums/-6-5-grendel-ammunition-reloading/505974-powder-sensitivity-test-in-an-18”-6-5-grendel |
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"The ammunition was stored outside from the previous day and I used environmental data from the National weather service at an airport approximately four miles from my residence. I also used my thermometers to try and get accurate ambient temperatures." I don't understand how your test was conducted. Did you have any direct measurement of temperature for the rounds being fired - no thermocouples, no IR temp readings? How were your thermometers used to define temperatures? Tell me about the sun lighting conditions. How did you get each of the temperatures? |
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Originally Posted By Trollslayer: "The ammunition was stored outside from the previous day and I used environmental data from the National weather service at an airport approximately four miles from my residence. I also used my thermometers to try and get accurate ambient temperatures." I don't understand how your test was conducted. Did you have any direct measurement of temperature for the rounds being fired - no thermocouples, no IR temp readings? How were your thermometers used to define temperatures? Tell me about the sun lighting conditions. How did you get each of the temperatures? I did not do a scientific test. I shot five different powders with different bullets in 6.5 Grendel on my property beside my house. I shot five rounds of each specific load and captured the velocities with my Athlon chronograph. I set the chronograph up at the same location for each time I shot at different temperatures. I used the National Weather Service weather reporting station at an airport four miles from my house. The ammunition was stored out side my house in a shaded area. I used consumer grade thermometers plus the NWS data to shoot at the different temperatures. I do not own IR thermometer and did not physically measure the temperature of the cartridge temperature prior to shooting. I’m retired and decided to test my reloaded ammunition at 10* intervals. Watching the NWS forecast I tried to conduct the test on days where the temperature was forecast to go to my targeted temperature. I watched the NWS current data and shot at the temperature where I wanted to collect the data. I watched my outdoor thermometer from my home indoor/outdoor thermometer and the NWS service temperature. When the temperature got to 18* for example I was outside and shot the twenty five 6.5 Grendel rounds and saved the chronograph data. I was interested in the potential difference in velocities at different temperatures and decided to share my results. I’m an old retired guy with an interest in firearms. This was a simple project I did to satisfy my own curiosity. I have saved the dates, times and weather data for each time I shot the twenty five 6.5 Grendel cartridges. I decided to use five rounds with each powder to keep cost down. |
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The weather has cooperated and I finally got good conditions to test the five loads at 88 degrees. I added the data to the charts above. I took care not to let the ammunition set in direct sunlight. I followed the same procedure as previous days. All brass looks good with no signs of pressure. I have the temperature written with a black marker on all previously fired cases separated by the particular powder used for future reference. |
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The temperature got up to 93* today and there has only been one day where the temperature hit 98* this summer and I wasn’t home to conduct the test. The scheduled high tomorrow is supposed to be 95* so I decided to shoot today even though there is only a five degree increase in temperature from my last day at 88*. I’ll set up tomorrow in the event it hits 98*. 08-15-2026 Temperature Stability Test 93* F, Humidity 54%, Barometric Pressure 30.09”, Dew Point 74* 2:29 PM CFE223, 123 grain Nosler Custom Competition, 31.0 grains, CCI450, Hornady Brass Avg. 2458.4, Min 2410.8, Max 2489.2, SD 27.6, ES 78.4, KE 1650.3 1. 2482.0 2. 2489.2 3. 2457.3 4. 2452.8 5. 2410.8 2:33 PM Shooters World 31.0 grains 123.0 grain SST, CCI450, new Hornady Brass Avg. 2544.8, Min 2521.0, Max 2563.0, SD 15.4, ES 42.0, KE 1768.4 1. 2543.6 2. 2563.0 3. 2559.4 4. 2521.0 5. 2537.1 2:36 PM A2520, 29.5 grains, 123 grain SST, CCI450, New Hornady Brass Avg. 2393.1, Min 2378.0, Max 2407.2, SD 10.8, ES 29.2, KE 1563.9 1. 2378.0 2. 2398.3 3. 2407.2 4. 2382.9 5. 2399.3 2:38 PM AR Comp 26.7 grains, 120 grain Nosler Ballistic Tip, CCI450, New Hornady Brass Avg. 23.19.1, Min 2300.9, Max 2330.7, SD 10.8, ES 29.9, KE 1432.8 1. 2300.9 2. 2315.9 3. 2318.6 stove pipe failure to completely eject 4. 2330.7 5. 2329.4 2:41 PM IMR8208XBR 26.4 grains 107 grain SMK, CCI450, Hornady Brass Avg. 2391.3, Min 2363.8, Max 2422.6, SD 19.0, ES 58.7, KE 1355.6 1. 2398.0 2. 2386.8 3. 2385.2 4. 2422.6 5. 2363.8 |
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According to the National Weather Service the temperature was 98* when I captured the velocities today. The velocities didn’t show any significant increase from my previous 93* day of collecting velocities. I keep my ammunition in the shade but I can’t say if the weather service thermometer is affected by direct sunlight. Regardless I used the same procedure today for collecting velocities as I have on days at the other recorded temperatures. I noticed a few firing pin indentations looked a little deeper and looked black in the bottom of the firing pin indention. No primers were pierced and the brass didn’t show any pressure signs. I did encounter a failure to feed between the third and fourth round of CFE223. I was using the same 17 round E-Lander as I did on other occasions. I also encountered a failure to feed on the fourth round of AR Comp. At higher temperature the AR Comp tends to produce less pressure than at colder temperatures closer to zero. The failure to feed could be a magazine issue but I don’t think so. I had my CFE223 loaded with Nosler 123 grain Custom Competition and the bullets were seated close to mag body so a bullet tip might have been dragging on the inside of the mag body contributing to the failure to feed. I updated the previous post in this thread with the 98* velocity. |
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Powder Temperature sensitivity test 8-31-2026 Temp. 98*, Humidity 38%, Barometric Press. 30.08”, Dewpoint 68* 13:18 CFE 223 31.0 grains, 123 grain Nosler CC, CCI450, Used Hornady Brass Avg. 2448.7, min. 2431.1, max. 2457.7, SD 9.5, ES 26.6, KE 1637.3 1. 2456.4 2. 2448.8 3. 2449.5 4. 2431.1 (failure to feed) 5. 2457.7 13:22 Shooters World Match Rifle, 31.0 grains, 123 grain SST, CCI 450, New Hornady Brass Avg. 2551.7, min. 2544.3, max. 2559.7, SD 5.6, ES 15.4, KE 1778.0 1. 2559.7 2. 2552.2 3. 2555.1 4. 2554.3 5. 2547.2 13:24 Accurate 2520, 29.5 grains, 123 grain SST, CCI450, New Hornady Brass Avg. 2388.8, min. 2373.7, max. 2397.0, SD 8.1, ES 23.3, KE 1558.3 1. 2392.1 2. 2397.0 3. 2388.5 4. 2373.7 5. 2393.0 13:25 AR Comp, 26.7 grains, CCI450, 123 grain SST, New Hornady Brass Avg. 2324.0, min. 2311.4, max. 2339.6, SD 10.9, ES 28.2, KE 1438.8 1. 2313.0 2. 2339.6 3. 2323.5 4.2311.4 (failure to feed) 5. 2332.3 13:30 IMR8208XBR 26.8 grains, CCI450, 107 grain Sierra Match King, Used Hornady Brass Avg. 2378.8, min. 2355.6, max. 2393.0, SD 12.8, ES 37.4, KE 1344.2 1. 2387.1 2. 2377.3 3. 2380.9 4. 2355.6 5. 2393.0 |
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Thanks for responding! I’ve been curious about velocity changes in different temperatures between different powders in calibers other than 5.56 and 7.62x51. I just thought I’d share my results. It would’ve been better had I shot ten or twenty round strings at each temperature but that would’ve been cost prohibitive. I checked the temperature to the next National Weather Service reporting station for the same date and time and both reported 98*. There is a twelve mile distance between these two airports with NWS data collection. |
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